At the end of thePleistocene(around 10,000 B.C.), the technologies of food production may have already been employed on the fringes of the rain forests of western and central Africa, where thecommonuse of suchrootplants as the African yam led people torecognizethe advantages of growing their own food. The yam can easily be resprouted if the top is replanted. Thisprimitiveform of "vegeculture" (cultivationofrootand tree crops) may have been theeconomictradition onto which thecultivationof summerrainfallcerealcrops was grafted as it came into use south of the grassland areas on the Sahara's southern borders.

As the Sahara dried up after 5000 B.C.,pastoralpeoples (cattleherders) moved southward along major watercourses into the savannabeltof West Africa and the Sudan. By 3000 B.C., just asancientEgyptiancivilizationwas coming into being along the Nile, they had settled in the heart of the East African highlands far to the south. The East African highlands areidealcattlecountry and the home today of such famous cattle-herding peoples as the Masai. The highlands were inhabited by hunter-gatherers living around mountains near the plains until about 3300 B.C., when the firstcattleherders appeared. Thesecattlepeople may have moved between fixed settlements during the wet and dry seasons, living off hunting in the dry months and their ownlivestockandagricultureduring the rains.

As was the case elsewhere,cattleweredemandinganimals in Africa. They required water atleastevery 24 hours and large tracts ofgrazinggrass if herds of any size were to be maintained. The secret was the carefulselectionofgrazingland, especially in environments whereseasonalrainfallled tomarkeddifferences in grazequalitythroughoutthe year. Evenmodestcattleherds required plenty of land andconsiderablemobility. Toacquiresuch land often required moving herdsconsiderabledistances, even from summer to winter pastures. At the same time, thecattleowners had to graze theirstockin tsetse-fly-free areas The only protection against human and animal sleeping sickness, adiseasecarried by the tsetse fly, was toavoidsettling or farming such areas -  aconstraintseverelylimiting the movements of cattle-owning farmers in eastern and central Africa. As a result, smallcattleherdsspreadsouth rapidly in areas where they could be grazed. Long beforecerealagriculturetook hold far south of the Sahara, some hunter-gatherer groups in the savanna woodlands of eastern and southern Africa may have acquiredcattle, and perhaps otherdomesticatedanimals, by giftexchangeorthroughraids on herding neighbors.

Contrarytopopularbelief: there is no suchphenomenonas "pure" pastoralists, a society that subsists on its herds alone. The Saharan herders who moved southward toescapedroughtwere almost certainly also cultivating sorghum, millet; and othertropicalrainfallcrops. By 1500 B.C.,cerealagriculturewaswidespreadthroughoutthe savannabeltsouth of the Sahara. Small farming communities dotted the grasslands and forest margins of eastern West Africa, all of them depending on what is called shiftingagriculture. This form ofagricultureinvolved clearing woodland, burning the felledbrushover the clearedplot, mixing the ash into the soil, and then cultivating the prepared fields. After a few years, the soil was exhausted, so the farmer moved on, exploiting new woodland and leaving the abandoned fields to liefallow. Shiftingagriculture, often called slash-and-burn, was highlyadaptivefor savanna farmers without plows, for it allowedcerealfarming with theminimalexpenditure of energy.

Theprocessof clearance and burning may have seemed haphazard to the uninformed eye, but it was not. Except infavoredareas, such as regularly inundated floodplains:tropicalAfrica's soils were of onlymoderateto lowfertility. The art of farming was careful soilselection, that is, knowing which soils were light and easily cultivable, could bereadilyturned with small hoes, and wouldmaintaintheirfertilityover several years' planting, forcerealcrops rapidly removenitrogenand other nutrients from the soil. Once it had taken hold: slash-and-burnagricultureexpanded its frontiers rapidly as village after village took up new lands, movingforwardso rapidly that one expert has estimated it took ameretwo centuries to cover 2,000 kilometers from eastern to southern Africa.

Questions:
question_stem: According to paragraph 1, which of the following is true of early food production by the end of the Pleistocene?
choices: tag: A
text: In certain areas of western and central Africa, some people were already growing root plants such as yams.

tag: B
text: The cultivation of cereal crops had already been used effectively and widely by people living on the fringes of rain forests.

tag: C
text: Sophisticated forms of "vegeculture" were introduced for the first time in central and western Africa by people from the Sahara's southern borders.

tag: D
text: The cultivation of root and tree crops replaced the cultivation of cereal crops because of decreasing summer rainfall in grassland areas.
answer_key: A
explanation: 【题目翻译】根据第1段，下列哪一项对于更新世末的早期粮食生产是正确的？
A：在非洲西部和中部的某些地区，一些人已经在种植山药等根茎植物。

B：种植谷类作物已经被生活在热带雨林边缘的人们广泛有效地利用。

C：来自撒哈拉南部边界的人们首次在中非和西非引进了先进的“草业”形式。

D：由于草原地区夏季降雨量减少，根和树作物的种植取代了谷类作物的种植。

【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。

【关键词定位】：根据关键词“early food production by the end of the Pleistocene”,定位到 Passage 1第1句，原句为“At the end of the Pleistocene (around 10,000 B.C.), the technologies of food production may have already been employed on the fringes of the rain forests of western and central Africa, where the common use of such root plants as the African yam led people to recognize the advantages of growing their own food.”
意思是“在更新世的末期（约公元10000 ），粮食生产技术可能已经在西部和中部非洲的雨林中使用，在那里，在非洲的普通用途的基础上，非洲的老年人能够对其自己的食物产生影响。”。

【逻辑分析】是问更新世末和早期粮食生产之间的关系。

【选项分析】
A 选项：在西非和中非的某些地方，有些人已经开始种植根茎类植物，例如山药。根据关键词“root plant”和“yams”定位到第一段第一句的后半句“……where the common use of such root plants as the African yam led people to recognize the advantages of growing their own food.”这句话说明当时人类确实已经开始种植山药等根茎类作物了。故 A 选项正确。 
B 选项：居住在热带雨林边缘的人已经高效并广泛地种植了谷类作物。错误，因为文中只提到种植块根植物和树本植物，谷类作物当时还没开始种植，所以 B 选项与原文矛盾。排除。
C 选项：“蔬菜栽培”的种植方法是由撒哈拉沙漠南部边界的人第一次引入非洲中部和西部地区的。错误，因为文中最后一句只说“……as it came into use south of the grassland areas on the Sahara's southern borders.” 这种种植技术已经在撒哈拉沙漠南部边界地区的草原南部被使用。但是没有说这些地区的人将这一技术引入非洲中部和西部地区，故 C 选项未提及，排除。 
D 选项：块根植物和树本植物的种植取代了谷类植物的种植，因为草原地区的降水量越来越少。这一信息在原文中完全未提及，故排除。

question_stem: Paragraph 2 mentions all of the following as developments in Sub-Saharan Africa from 5000 to 3000 B.C. EXCEPT
choices: tag: A
text: The Sahara dried up.

tag: B
text: Ancient Egyptian civilization started to form along the Nile.

tag: C
text: The inhabitants of the East African highlands gave up hunting when cattle herders arrived.

tag: D
text: Pastoral peoples moved through the savanna belt to settle in the East African highlands.
answer_key: C
explanation: 【题目翻译】第2段提到了撒哈拉以南非洲从公元前5000年到3000年的发展情况，但除了哪个以外？
A 撒哈拉沙漠干涸了。

B 古埃及文明开始沿尼罗河形成。

C 当牧牛人到达时，东非高地的居民放弃了狩猎。

D 牧民们穿过大草原地带，在东非高地定居。

【判定题型】：根据题干中出现的大写“EXCEPT”/"NOT" 等其他明显表示否定的词，可以判定本题为否定事实信息题，需要找出与原文信息不符的那个答案。

【关键词定位】：根据题干关键词“5000 to 3000B.C.”定位于“By 3000 B.C., just as ancient Egyptian civilization was coming into being along the Nile, they had settled in the heart of the East African highlands far to the south. ”,可以将出题范围锁定在 Passage 2 。

【选项分析】
A 选项：撒哈拉地区干涸了。第二段第一句说“As the Sahara dried up after 5000 B.C.……”这句话证明 A 选项符合原文，故 A 选项排除。 
B 选项：古代埃及文明在尼罗河流域发源。第二段第2句说“By 3000 B.C., just as ancient Egyptian civilization was coming into being along the Nile……”这句话证明 B 选项符合原文，故 B 选项排除。 
C 选项：当游牧民族到来的时候，东非高地的原住民放弃了狩猎。原文说“The highlands were inhabited by hunter-gatherers living around mountains near the plains until about 3300 B.C., when the first cattle herders appeared.”这句话说直到大约公元前3300年，第一批牧牛人出现时，高地上居住着狩猎采集者，他们居住在平原附近的山区。但是文中没有提到这些原住民在游牧民族到来后就放弃了狩猎，故 C 选项在文中未提及，为正确答案。 
D 选项：游牧民族穿过了稀树草原带，在东非高地定居。对应第二段第1、2句“pastoral peoples (cattle herders) moved southward along major watercourses into the savanna belt of West Africa and the Sudan……settled in the heart of the East African highlands far to the south.”证明 D 选项是符合原文的，故 D 选项排除。

question_stem: Which of the following can be inferred from paragraph 2 about the pastoral peoples in the East African Highlands around 3300 B.C.?
choices: tag: A
text: They lived around the mountains and rarely descended into the plains.

tag: B
text: They relied on different food sources during dry months than they did during wet months.

tag: C
text: Their settlements were larger than those of pastoral peoples in West Africa and the Sudan.

tag: D
text: They obtained food from nearby hunter-gatherer communities during wet months.
answer_key: B
explanation: 【题目翻译】从公元前3300年左右关于东非高地牧民的第2段中可以推断出以下哪一个？
A 他们住在群山周围，很少下到平原去。

B 他们在干燥月份依赖的食物来源不同于潮湿月份。

C 他们的定居点比西非和苏丹的牧民要大。

D 他们在潮湿的月份从附近的狩猎-采集社区获得食物。

【判定题型】：根据题干中出现的关键词“imply”/“infer”/“suggest”等其他表示推断的词，判定本题为推理题。

【关键词定位】根据题干中的关键年份“3300 B.C.”可以直接定位到这句话“The highlands were inhabited by hunter-gatherers living around mountains near the plains until about 3300 B.C., when the first cattle herders appeared.”

【逻辑分析】直到大约公元前3300年，第一批牧牛人出现时，高地上居住着狩猎采集者，他们居住在平原附近的山区。最后一句话也是在描述游牧民族到达高地后的生活模式：在旱季和雨季，这些放牧人可能在固定的定居点之间移动，在旱季他们过着打猎的生活，在雨季靠畜牧和种植为生。

【选项分析】
A 选项：他们住在山的附近，很少到平原去。这句话是描述说高地上原来居住的那些“hunter-gatherers”，不是在描述 pastoral people，而且文中也没有说这些“hunter-gatherers”很少来到平原上。故 A 选项直接排除。 
B 选项：他们在旱季的食物来源要比在雨季的食物来源更丰富。我们可以从文中最后一句话推理出 B 选项是正确的。最后一句说：这些游牧民族在旱季过着打猎的生活，在雨季靠畜牧和种植为生。打猎获得的食物肯定更丰富，而靠畜牧和种植，食物来源相对比较单一，故 B 选项正确。 
C 选项：他们的定居点要比西非和苏丹的游牧民族大。文中没有提到定居点规模大小的信息，故 C 选项排除。 
D 选项：在雨季，他们从附近的依靠采集狩猎卫生的原住民那边获得食物。文中未提到该信息，故排除。

question_stem: The word "modest" in the passage is closest in meaning to
choices: tag: A
text: small

tag: B
text: strong

tag: C
text: good

tag: D
text: typical
answer_key: A
explanation: 【题目翻译】文章中“modest”这个词的意思最接近于
A 选项: small,意思是“小的”
B 选项：strong，意思是“强壮的” 
C 选项：good，意思是“好的”
D 选项：typical，“一贯的；平常的”

【判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】：根据关键词“modest”,定位到原句“Even modest cattle herds required plenty of land and considerable mobility.”

【词汇解析】：词汇“modest”的意思是“适中的”,带入到原句中，原句的意思是“即使是规模适中的牛群也需要大片的土地和相当大的可移动性。”

【选项分析】
A 选项: small,意思是“小的”，意思最接近，故为正确选项。 
B 选项：strong，意思是“强壮的”，意思不符，故排除。 
C 选项：good，意思是“好的”，意思不符，故排除。 
D 选项：typical，“一贯的；平常的”，意思不符，故排除。

question_stem: Paragraph 3 mentions all of the following as reasons that raising cattle in Africa was demanding EXCEPT:
choices: tag: A
text: Cattle had to drink frequently.

tag: B
text: Cattle needed large areas of good-quality grazing grass.

tag: C
text: Cattle required a great deal of movement from one season to the next.

tag: D
text: Cattle suffered from sleeping sickness after the herds spread south.
answer_key: D
explanation: 【题目翻译】第3段提到以下所有在非洲饲养牛的理由，除了哪个之外：
A 牛不得不经常喝水。

B 牛需要大面积优质牧草。

C 牛从一个季节到下一个季节需要大量的移动。

D 牛群向南扩散后，牛群得了昏睡病。

【判定题型】：根据题干中出现的大写“EXCEPT”/"NOT" 等其他明显表示否定的词，可以判定本题为否定事实信息题，需要找出与原文信息不符的那个答案。

【关键词定位】：根据题干关键词“raising cattle in Africa was demanding”,可以将出题范围锁定在 Passage 3 的第一二句话。As was the case elsewhere, cattle were demanding animals in Africa. @@@@They required water at least every 24 hours and large tracts of grazing grass if herds of any size were to be maintained. 

【选项分析】
A 选项：牛需要频繁地喝水。可以定位到第三段第2句话“ They required water at least every 24 hours and large tracts of grazing grass if herds of any size were to be maintained.”这句话说牛群至少每24小时就需要喝水，说明 A 选项符合原文，故排除。 
B 选项：牛群需要大片高质量的牧草。根据关键词“grazing grass”同样定位到第三段第2句，所以 B 选项符合原文，故排除。 
C 选项：从一个季节转变到下一个季节时，牛群需要移动很远的距离。定位到这句话“To acquire such land often required moving herds considerable distances, even from summer to winter pastures.”这句话表明，牛群经常需要移动相当远的距离，从夏季牧场迁移到冬季牧场。所以这里 C 选项符合原文，故排除。 
D 选项：牛群迁移到南部之后，开始患上昏睡病。但是原文中说的是，为了避免感染昏睡病，牛群迅速向南部地区迁移。所以南部是没有致病的舌蝇出没的。故 D 选项与原文矛盾，为正确答案。

question_stem: The word "severely" in the passage is closest in meaning to
choices: tag: A
text: gradually

tag: B
text: permanently

tag: C
text: indirectly

tag: D
text: very seriously
answer_key: D
explanation: 【题目翻译】文章中“severely”这个词的意思最接近于
A 选项：gradually,意思是“逐步地，渐渐地”
B 选项：permanently,意思是“永久地，长期不变地” 
C 选项：indirectly,意思是“间接地” 
D 选项：very seriously，意思是“非常严重地”

【判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】：根据关键词“severely”,定位到原句词汇所在句“……a constraint severely limiting the movements of cattle-owning farmers in eastern and central Africa.”

【词汇解析】：词汇“severely”的意思是“严重地”,带入到原句中，原句的意思是……对东非和中非地区的牧民来说，这个办法严重低限制了他们的迁移。”

【选项分析】
A 选项：gradually,意思是“逐步地，渐渐地”,意思不符，故排除。 
B 选项：permanently,意思是“永久地，长期不变地”,意思不符，故排除。 
C 选项：indirectly,意思是“间接地”，意思不符，故排除。 
D 选项：very seriously，意思是“非常严重地”，意思符合，故为正确答案。

question_stem: According to paragraph 3, the presence of the tsetse fly in eastern and central Africa caused which of the following?
choices: tag: A
text: People in the sub-Saharan region began to focus more on the cultivation of cereal crops than in maintaining livestock.

tag: B
text: Raids among neighboring cattle herders increased dramatically.

tag: C
text: Cattle herders spread south where they could graze their stock in tsetse-fly-free areas.

tag: D
text: Most hunter-gatherer groups limited their food collection to the tsetse-fly-free areas south of the Sahara.
answer_key: C
explanation: 【题目翻译】根据第3段，舌蝇在东部和中部非洲的存在导致下列哪一个？
A：撒哈拉以南非洲地区的人们开始把更多的精力放在种植谷类作物上，而不是养活牲畜上。
B：邻近的牧民的袭击急剧增加。
C：牧牛人向南散布，在没有舌蝇的地方放牧牲畜。
D：大多数狩猎-采集组织将他们的食物收集限制在撒哈拉以南无舌蝇的地区。

【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。

【关键词定位】根据题干中的关键词“tsetse fly”，可以定位到第三段倒数2、3、4句“At the same time, the cattle owners had to graze their stock in tsetse-fly-free areas ……As a result, small cattle herds spread south rapidly in areas where they could be grazed.”

【逻辑分析】题目问，在东非和中非的舌蝇会造成什么后果？这三句话的内容都是在讲舌蝇和舌蝇带来的后果。题干中“caused”一词是在问结果，所以我们在文中找到关键词“as a result”，后面的内容就是结果，即小部分牛群迅速地向南部地区迁移，在那里人们可以放牧。

【选项分析】
A 选项：撒哈拉以南非洲地区的人民开始花更多精力培养谷物，而不是饲养牛群。错误，因为文中没有提到两者之间的比较关系，人们即种植谷物，也饲养牛群。其次，这不是舌蝇造成的影响。 
B 选项：邻里之间抢夺牛群的情况愈演愈烈。对应第三段最后一句“Long before cereal agriculture took hold far south of the Sahara ……by gift exchange or through raids on herding neighbors.”但是这句话只是为了说明狩猎采集者获得牲畜的方式——作为礼物交换，或者通过劫掠放牧的邻居来获得这些牲畜。这并不是舌蝇造成的影响。故 B 选项排除。
C 选项：正确表达了原文的意思，所以 C 选项正确。 
D 选项：大部分的狩猎采集者将他们的觅食范围限定在了撒哈拉南部没有舌蝇的地带。错误，因为文章没有提到该信息。

question_stem: Paragraph 4 indicates which of the following about shifting agriculture?
choices: tag: A
text: It allowed farmers to cultivate cereal crops without reducing the size of their herds.

tag: B
text: It allowed farmers to cultivate a variety of crops at the same time.

tag: C
text: It enabled farmers to cultivate crops with minimal equipment and effort.

tag: D
text: It enriched the soil and produced large yields of crops over the years.
answer_key: C
explanation: 【题目翻译】第4段指出以下哪一个是关于农业转移的？
A：它允许农民种植谷类作物，而不会减少牲畜的数量。
B：它允许农民同时种植各种作物。
C：它使农民能用最少的设备和努力来种植庄稼。
D：多年来，它使土壤肥沃，作物产量大。

【判定题型】题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。

【关键词定位】：根据关键词“hifting agriculture”,定位到 Passage 4 最后一句话，原句为“shifting agriculture, often called slash-and-burn, was highly adaptive for savanna farmers without plows, for it allowed cereal farming with the minimal expenditure of energy.
”，意思是：“经常被称作“刀耕火种”的转型农业，对于没有犁的大草原农民来说适应性很强，因为它允许以最少的能源消耗进行谷物农业。”。

【逻辑分析】文章表达的两者的关系是：“刀耕火种”的转型农业很适合没有犁的大草原农民。

【选项分析】
A 选项：它使农民在不需要减少牧群规模的情况下耕种谷物。错误。第四段没有提及该信息。 
B 选项：它使农民可以同时种很多种农作物。错误，因为第四段没有提及该信息。文中只提到“The Saharan herders who moved southward to escape drought were almost certainly also cultivating sorghum, millet; and other tropical rainfall crops.”但这句话说南迁移的牧民，他们肯定也种植高粱、小米和其他热带降雨作物。但是并没有说他们用轮耕法同时耕种这些农作物，故 B 选项排除。 
C 选项：它使农民可以用最少的装备和精力来耕种。根据选项中的关键词“minimal”定位到第四段最后一句“Shifting agriculture, often called slash-and-burn, was highly adaptive for savanna farmers without plows, for it allowed cereal farming with the minimal expenditure of energy.”这句话说轮耕法，也被称为“刀耕火种”，高度适用于没有犁的稀树草原地区的农民，因为这种方法能够消耗最少的能量来种植谷类。所以 C 选项符合原文，为正确答案。 
D 选项：它能使土壤肥沃，生产出大量的粮食。错误，因为第四段没有提及该信息。

question_stem: The word "exploiting” in the passage is closest in meaning to
choices: tag: A
text: making use of

tag: B
text: finding

tag: C
text: destroying

tag: D
text: looking for
answer_key: A
explanation: 【题目翻译】文章中的“exploiting”一词最接近于下列哪个选项？
A 选项：making use of 的意思是“利用”
B 选项：finding 的意思是“找到” 
C 选项：destroying 的意思是“破坏”
D 选项：looking for 的意思是“寻找”

【判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】：根据关键词“exploiting,定位到原句“After a few years, the soil was exhausted, so the farmer moved on, exploiting new woodland and leaving the abandoned fields to lie fallow.”

【词汇解析】：词汇“exploiting”的意思是“开采、利用”,带入到原句中，原句的意思是“几年后，土地耗尽了养分，于是农民们继续前进，开辟新的林地，让原来的荒地休耕。”

【选项分析】
A 选项：making use of 的意思是“利用”，意思最接近，故为正确答案。 
B 选项：finding 的意思是“找到”，意思不符，故排除。 
C 选项：destroying 的意思是“破坏”，意思不符，故排除。 
D 选项：looking for 的意思是“寻找”，意思不符，故排除。

question_stem: The word "readily" in the passage is closest in meaning to
choices: tag: A
text: completely

tag: B
text: easily

tag: C
text: properly

tag: D
text: regularly
answer_key: B
explanation: 【题目翻译】文章中的“readily”一词最接近于以下哪个选项？
A 选项：completely 的意思是“完全地；完整地”。 
B 选项：easily 的意思是“简单地” 
C 选项：properly 的意思是“适当地；正确地”
D 选项：regularly 的意思是“定期地；有规律地”

【判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】：根据关键词“readily”,定位到原句“The art of farming was careful soil selection, that is, knowing which soils were light and easily cultivable, could be readily turned with small hoes”。

【词汇解析】：词汇“readily”的意思是“开采、利用”,带入到原句中，原句的意思是“农业的艺术就在于小心地选择土地，那就是说，知道哪些土壤是轻土壤，容易耕种，很容易用小锄头翻种。”

【选项分析】
A 选项：completely 的意思是“完全地；完整地”,意思不符，故排除。 
B 选项：easily 的意思是“简单地”，意思符合，故为正确答案。 
C 选项：properly 的意思是“适当地；正确地”,意思不符，故排除。 
D 选项：regularly 的意思是“定期地；有规律地”

question_stem: Which of the following best describes the relationship of paragraph 5 to paragraph 4?
choices: tag: A
text: Both paragraphs compare the effectiveness of cereal agriculture and cattle herding as food-production strategies in the sub-Saharan regions.

tag: B
text: Paragraph 5 challenges the ideas in paragraph 4 about the relative importance of shifting agriculture in the sub-Saharan regions.

tag: C
text: Both paragraphs emphasize the idea that agricultural practices south of the Sahara took a very long time to develop.

tag: D
text: Paragraph 5 provides further details about the practice of shifting agriculture south of the Sahara presented in paragraph 4.
answer_key: D
explanation: 【题目翻译】下列哪一项最能说明第5段与第4段的关系？
A：这两段都比较了撒哈拉以南地区谷物农业和畜牧业作为粮食生产战略的有效性。

B：第5段质疑第4段关于撒哈拉以南地区农业转移的相对重要性的观点。

C：这两段都强调了撒哈拉以南的农业实践需要很长时间才能发展的观点。

D：第5段提供了关于第4段提出的将农业转移到撒哈拉以南的做法的进一步细节。

【判定题型】：根据题目问法，题目询问 xxx 组成或构成方式/段落与段落的关系/某一段在全文中所起的作用，故判断本题为组织结构题。

【内容分析】题目问，第四段和第五段的关系是什么？我们先分别来看第四段和第五段的内容。第四段主要讲了牧民们采用轮耕法，即“刀耕火种”发，用最少的设备和精力来耕种。而第五段进一步分析了“刀耕火种”法的优点以及传播。

【选项分析】
A 选项：两段都在比较撒哈拉以南地区谷物农业和畜牧养殖作为食物生产方式的有效性。错误，因为四、五两段主要是在将谷物种植，且没有将种植农作物与畜牧业进行对比，故 A 选项排除。 
B 选项：第五段质疑了第四段所持的关于撒哈拉以南地区轮耕法的相对重要性的观点。错误，因为第五段没有任何反驳第四段观点的迹象，故 B 选项排除。 
C 选项：两段都在强调撒哈拉以南地区的农业生产是经过很长时间才发展起来的。错误，因为第四段和第五段都没有强调农业生产花很长时间发展，只有第五段的最后一句说专家预计轮耕法在2个世纪的时间里就覆盖了东非和西非2000平方公里的土地。但是这是在说明轮耕法发展的迅速，并不是强调它的发展要花很长时间。故 C 选项排除。 
D 选项：第四段中提到撒哈拉以南地区实行农耕法，第五段对此提供了更多的细节说明。正确，符合原文的篇章逻辑。故 D 选项正确。