Research has shown that certain minerals are required by plants for normal growth anddevelopment. The soil is thesourceof these minerals, which are absorbed by the plant with the water from the soil. Evennitrogen, which is a gas in its elementalstate, isnormallyabsorbed from the soil asnitrateions. Some soils are notoriouslydeficientin micro nutrients and arethereforeunable to support most plant life. So-calledserpentine soils, for example, aredeficientincalcium, and only plants able totoleratelow levels of thismineralcansurvive. In modernagriculture,mineraldepletion of soils is amajorconcern, since harvesting crops interrupts the recycling of nutrients back to the soil.

Mineraldeficiencies can often be detected byspecificsymptoms such as chlorosis (loss ofchlorophyllresulting in yellow or white leaftissue), necrosis (isolateddead patches), anthocyaninformation(developmentof deep redpigmentationof leaves orstem), stunted growth, anddevelopmentof woodytissuein anherbaceousplant. Soils are most commonlydeficientinnitrogenandphosphorus. Nitrogen-deficient plantsexhibitmany of the symptoms just described. Leaves develop chlorosis; stems are short andslender, and anthocyanin discoloration occurs on stems, petioles, andlowerleaf surfaces. Phosphorus-deficient plants are often stunted, with leaves turning acharacteristicdark green, often with theaccumulationof anthocyanin. Typically, older leaves are affected first as thephosphorusis mobilized to young growingtissue. Irondeficiencyis characterized by chlorosis between veins in young leaves.

Much of the research onnutrientdeficiencies is based on growing plants hydroponically, that is, in soillessliquidnutrientsolutions. Thistechniqueallows researchers to create solutions that selectivelyomitcertain nutrients and thenobservethe resulting effects on the plants. Hydroponics has applications beyondbasicresearch, since it facilitates the growing of greenhouse vegetables during winter. Aeroponics, atechniquein which plants aresuspendedand the roots misted with anutrientsolution, is anothermethodfor growing plants without soil.

Whilemineraldeficiencies can limit the growth of plants, an overabundance of certain minerals can betoxicand can also limit growth. Saline soils, which have high concentrations ofsodiumchloride and other salts, limit plant growth, and research continues tofocuson developing salt-tolerant varieties of agricultural crops. Research has focused on thetoxiceffects of heavy metals such aslead, cadmium,mercury, andaluminum; however,evencopperandzinc, which areessentialelements, can becometoxicin high concentrations. Although most plants cannotsurvivein these soils, certain plants have theabilitytotoleratehigh levels of these minerals.

Scientists have known for some time that certain plants, called hyperaccumulators, canconcentrateminerals at levels a hundredfold or greater than normal. Asurveyof known hyperaccumulators identified that 75 percent of them amassednickel, cobalt,copper,zinc, manganese,lead, and cadmium are other minerals of choice. Hyperaccumulators run the entire range of the plant world.They may be herbs, shrubs, or trees. Many members of the mustard family, spurge family,legumefamily, and grass family are top hyperaccumulators. Many are found intropicaland subtropical areas of the world, whereaccumulationof high concentrations of metals mayaffordsome protection against plant-eating insects and microbial pathogens.

Only recently have investigators considered using these plants to clean up soil andwastesites that have been contaminated bytoxiclevels of heavy metals–an environmentally friendlyapproachknown as phytoremediation. Thisscenariobegins with the planting of hyperaccumulatingspeciesin thetargetarea, such as an abandonedmineor anirrigationpond contaminated byrunoff. Toxicminerals would first be absorbed by roots but later relocated to thestemand leaves. Aharvestof the shoots would remove thetoxiccompounds off site to be burned or composted torecoverthe metal forindustrialuses. After several years ofcultivationandharvest, the site would be restored at acostmuchlowerthan the price ofexcavationand reburial, thestandardpractice forremediationof contaminated soils. For examples, infieldtrials, the plantalpinepennycress removedzincand cadmium from soils near azincsmelter, and Indian mustard, native to Pakistan and India, has beeneffectivein reducing levels of selenium salts by 50 percent in contaminated soils.

Questions:
question_stem: According to paragraph 1, what is true of plants that can grow in serpentine soil?
choices: tag: A
text: They absorb micronutrients unusually well.

tag: B
text: They require far less calcium than most plants do.

tag: C
text: They are able to absorb nitrogen in its elemental state.

tag: D
text: They are typically crops raised for food.
answer_key: B
explanation: B 以 serpentine soil 做关键词定位至倒数第二句，这种土壤钙质缺乏，只有对钙要求很低的植物可以生存。问题问什么样的植物能够生存，所以 B 正确。A 中 micronutrients 没说，C 的 nitrogen 和 elemental state 与问题无关，错；D 的 food 没说。

question_stem: The word “exhibit” in the passage is closest in meaning to
choices: tag: A
text: fight off

tag: B
text: show

tag: C
text: cause

tag: D
text: spread
answer_key: B
explanation: B exhibit: 显示，显出。A 是排斥，抵抗，摆脱；B 是展示，显示；C 是引起；D 是传播。所以 B 的 show 正确。

question_stem: According to paragraph 2, which of the following symptoms occurs in phosphorus-deficient plants but not in plants deficient in nitrogen or iron?
choices: tag: A
text: Chlorosis on leaves

tag: B
text: Change in leaf pigmentation to a dark shade of green

tag: C
text: Short, stunted appearance of stems

tag: D
text: Reddish pigmentation on the leaves or stem
answer_key: B
explanation: B, 以 phosphorus-deficient plants 做关键词定位至倒数第二句，说 phosphorus-deficient，磷缺乏的植物是容易倒的，并且叶子会变成暗绿色，B 是答案。A 中的 chlorosis 萎黄病，变色病没说；C 中的茎很短原文没说；D 中的 reddish pigmentation 原文没说。

question_stem: According to paragraph 2, a symptom of iron deficiency is the presence in young leaves of
choices: tag: A
text: deep red discoloration between the veins

tag: B
text: white or yellow tissue between the veins

tag: C
text: dead spots between the veins

tag: D
text: characteristic dark green veins
answer_key: B
explanation: B 以 iron deficiency 和 young leaves 做关键词定位至最后一句，chlorosis 变色病，萎黄病，所以 B 项的 white or yellow tissue 刚好对上。A 项的 deep red 没说，错；C 的 dead spots 原文没说，错；D 的 dark green 是缺乏磷的症状，不对。

question_stem: The word “facilitates” in the passage is closest in meaning to
choices: tag: A
text: slows down

tag: B
text: affects

tag: C
text: makes easier

tag: D
text: focuses on
answer_key: C
explanation: facilitate: 促进，帮助，使容易。A 是变慢；B 是影响；C 是使容易；D 是集中于。所以 C 的 makes easier 正确。对应原文:Hydroponics has applications beyond basic research, since it facilitates the growing of greenhouse vegetables during winter. 原句说 hydroponic 除了基本研究之外还有其他应用，就是实际上的应用，说怎么样了冬天里温室蔬菜的生长。从感情色彩上看，这个地方要的是一个正向词，A 的 slow down 和 B 的 affect 都不对。focus on 也不行，属于中性词，必须正向，所以答案是 make easier。

question_stem: According to paragraph 3, what is the advantage of hydroponics for research on nutrient deficiencies in plants?
choices: tag: A
text: It allows researchers to control what nutrients a plant receives.

tag: B
text: It allows researchers to observe the growth of a large number of plants simultaneously.

tag: C
text: It is possible to directly observe the roots of plants.

tag: D
text: It is unnecessary to keep misting plants with nutrient solutions.
answer_key: A
explanation: 以 nutrient deficiency 做关键词定位至第一句，但第一句只是给这个无土栽培下了个定义，第二句才开始说好处：This technique allows researchers to create solutions that selectively omit certain nutrients and then observe the resulting effects on the plants.使得 researchers 能够有意去掉某种营养，然后看效果，也就是 A 说的可以选择让植物吸收什么营养；其他三项都完全没说。

question_stem: The word “suspended” in the passage is closest in meaning to
choices: tag: A
text: grown

tag: B
text: protected

tag: C
text: spread out

tag: D
text: hung
answer_key: D
explanation: suspend: 悬垂，悬挂。A 是种植；B 是保护；C 是展开，铺开；D 是悬挂。所以 D 的 hung 是正确答案。对应原文:Aeroponics, a technique in which plants are suspended and the roots misted with a nutrient solution, is another method for growing plants without soil.原句中 acroponics 意思是空气种植法，acro 表示悬空，所以后面的解释是把植物怎么样，而且跟后面的 mist 并列，mist 混合。混合与成长是不能并列的，grow 错；同样 C 的铺开也不对；protect 是完全不靠谱的。

question_stem: Why does the author mention “herbs”, “shrubs”, and “trees”?
choices: tag: A
text: To provide examples of plant types that cannot tolerate high levels of harmful minerals.

tag: B
text: To show why so many plants are hyperaccumulators.

tag: C
text: To help explain why hyperaccumulators can be found in so many different places.

tag: D
text: To emphasize that hyperaccumulators occur in a wide range of plant types.
answer_key: D
explanation: 功能目的题，而且这句话中有个 they，指代前文，所以往前看，说 HA 在整个植物界分布广泛，后面的几种植物就是 HA 的例子，所以答案是 D。A 说 cannot tolerate 反了；原文没说到原因，所以 B/C 都错。

question_stem: The word “afford” in the passage is closest in meaning to
choices: tag: A
text: offer

tag: B
text: prevent

tag: C
text: increase

tag: D
text: remove
answer_key: A
explanation: afford: 给予，提供。A 是提供；B 是防止；C 是增加；D 是一处。所以 offer 提供，给出是正确答案。对应原文：Many are found in tropical and subtropical areas of the world, where accumulation of high concentrations of metals may afford some protection against plant-eating insects and microbial pathogens.很多物种都生长在热带及亚热带地区，那儿的高浓度金属可以怎么样保护植物免遭吃植物的昆虫的捕食。从原文看，高浓度的金属应该是起到了正面的作用。B 的 prevent 防止保护和 D 的 remove 去除保护肯定不对；increase 增加保护是在原有的基础上增加，原文没说原来就有保护，所以 increase 不对。

question_stem: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
choices: tag: A
text: Before considering phytoremediation, hyperaccumulating species of plants local to the target area must be identified.

tag: B
text: The investigation begins with an evaluation of toxic sites in the target area to determine the extent of contamination.

tag: C
text: The first step in phytoremediation is the planting of hyperaccumulating plants in the area to be cleaned up.

tag: D
text: Mines and irrigation ponds can be kept from becoming contaminated by planting hyperaccumulating species in targeted areas.
answer_key: C
explanation: C 这句话的主干部分并不长，such as 后面开始时举例部分，可以先忽略不看。主干说：这个方案由种植 species 开始。由…开始对应 C 选项的 first step，C 正确。A 中的 before 是没说的，原文一直在说这件事开始于什么什么，这件事之前干嘛没说；原文有个很难替换的词 HAS，而这个词在 B 答案中没有，所以 B 错；C 同义替换，正确；D 把 such as 里面的例子变成了句子的主要部分，改变了结构，错。

question_stem: It can be inferred from paragraph 6 that compared with standard practices for remediation of contaminated soils, phytoremediation
choices: tag: A
text: does not allow for the use of the removed minerals for industrial purposes

tag: B
text: can be faster to implement

tag: C
text: is equally friendly to the environment

tag: D
text: is less suitable for soils that need to be used within a short period of time
answer_key: D
explanation: D 以 contaminated soil 和 remediation 做关键词定位至倒数第二句，说经过若干年的耕种与收割之后，那个地方就会恢复，说明没有若干年就不能恢复，所以 D 正确。A/C 没有相关信息；B 说反，应该是传统的挖掘方法更快，新的种植物的方法慢。

question_stem: Why does the author mention “Indian mustard”?
choices: tag: A
text: To warn about possible risks involved in phytoremediation

tag: B
text: To help illustrate the potential of phytoremediation

tag: C
text: To show that hyperaccumulating plants grow in many regions of the world

tag: D
text: To explain how zinc contamination can be reduced
answer_key: B
explanation: 功能目的题，Indian mustard 做关键词定位至最后一句，这句话整个是个例子，而且之前的那句话也是个例子。再往前就是上题的那句话，也就是说经过若干年耕种与收割，那个地方就会变好，也就是这种方法有用，所以答案 B 正确。