The forked tongue of snakes has intrigued people formillennia, inspiring many hypotheses. In many cultures and religions, the forked tongue symbolizes malevolence and deceit. The first person known toinquireabout thefunctionalsignificanceof the forked tongue wasAristotle; he suggested that it would double the pleasure of sensations oftaste. By the beginning of the twentiethcentury, theconsensuswas that the snake’s tongue is a tactile organ; that is, the snake uses it to tap the ground much as ablindperson uses a cane.

In 1920 Browman suggested what seemed to be a winning hypothesis: When the snake retracts its tongue, the tips (or tines) of the forked tongue are inserted into openings on both sides of the roof of the mouth;throughthese openings chemical stimulireachspecialorgans that help snakesdetectsmells—the vomeronasal organs (VNO). These organs are highly developed in snakes, lizards, and many mammals. They are asecondsystem for detecting smells that appears to have evolvedspecificallytodetectpheromones, the chemical signals that animalssecreteas messages to other animals of theirspecies. Browman suggested that the forked tongue flicks out, picking up chemical signals, and then delivers these to the VNO. Thishypothesiswas widely accepted into the 1980s. Then X-ray movie studies of tongue flicks in snakes and lizards with forked tongues disproved thehypothesis; they showed that when the tongue is withdrawn into the mouth, it enters asheathand the tips do not go into the openings to the VNO. Instead, the chemical molecules are deposited on pads at the bottom of the mouth, and closing the mouth presses the pads and molecules against the VNO openings.

If the tongue is not forked to fit into the VNO, then whatfunctioncould the forkedshapeserve? Schwenk proposes asolutionthat encompasses observations from several fields—animalbehavior,ecology,sensoryphysiology, and neuroanatomy. He hypothesizes that the forked tongue allows the snake tosensechemical stimuli at two points simultaneously,therebygiving it theabilitytodetectdifferences in anodortrail. Obtaining twosimultaneousreadings enhances theabilityof the snake todetectthe edges ofodortrails, and thus to followpheromonetrails accurately. Thisabilityis important in seeking bothpreyand mates.

Thisspatialchemicalperceptionis like other systems forspatialperceptionthat are based onsimultaneousstimulationof two separatedsenseorgans—for example,auditorylocalization, which depends on differentialstimulationat the two ears. Similarly, the use of the two eyes permits stereovision.

Several kinds ofevidencesupport thehypothesisthat forked tongues evolved as chemosensoryedgedetectors toenhancetheabilityto followodortrails: (1) Snakes and lizardsspreadthe tines of their tongue apart when theyretrieveodormolecules, thendrawthe tines together when retracting the tongue. The greater the distance between sampling points, the better the animalssampledifferenceswithinanodortrail. (2) Lizards thatforagewidely have forked tongues, whereaslizardspecieswithout forked tonguestendnot toforagewidely. (3) Forked tongues have evolved independently atleasttwice in different families of reptiles, indicating their value as anadaptation. (4) In the snake nervous system, each tine of the tongue is linked to anucleusin the other side of the brain, and the twonucleiare linkedacrossthe two hemispheres. This arrangement issimilarto theanatomyofauditorycenters in mammals and birds that permits the computation of differences between what one ear hears and what the other ear hears and thus mediatesauditorylocalization.

Speciesin other orders have also evolved paired chemical receptors to guide individuals to mates orprey. For example,malegypsy moths have large,elaborate, odor-detecting antennae with which theytrackpotentialmates over large distances, and the antnestbeetle has spoon-shaped antennae extending from each side of the head with which it detects and follows the pheromones of the ants that are its food.

Questions:
question_stem: The word “secrete” in the passage is closest in meaning to
choices: tag: A
text: hide

tag: B
text: intend

tag: C
text: produce

tag: D
text: collect
answer_key: C
explanation: secrete vt.（1）（细胞，腺体，器官）分泌（物质）=produce；（2）隐藏，躲藏 = hide。
原文 pheromones, the chemical signals that animals secrete 中的 secrete 指动物分泌，取“分泌”之意，与 produce 同义，故选 C。"

question_stem: According to paragraph 2,what was discovered as a result of X-ray movie studies of snakes and lizards?
choices: tag: A
text: The two tines of the forked tongue flick out to pick up chemical signals.

tag: B
text: VNO are highly developed in snakes and lizards.

tag: C
text: Snakes and lizards cannot accurately detect the pheromones of animals of other species.

tag: D
text: The snake's tongue deposits chemical molecules on pads at the bottom of the snake's mouth.
answer_key: D
explanation: 题干提问“由 X-ray movie studies of snakes and lizards 可以 discovered 什么？”，即根据一个研究，得出相应的结论。定位原文最后两句：Then X-ray movie studies of tongue flicks … ... and closing the mouth presses the pads and molecules against the VNO openings. “他们的研究表明，当舌头缩入口腔时，它会进入护套，而尖端不会进入 VNO 的开口。相反，化学分子沉积在嘴底的垫片上，并且闭合嘴部将垫片和分子压在 VNO 开口上“，故选 D。ABC 在对应解题句中未提及。

question_stem: The word “simultaneously” in the passage is closest in meaning to
choices: tag: A
text: in a similar manner

tag: B
text: at the same time

tag: C
text: at some distance from each other

tag: D
text: with great skill
answer_key: B
explanation: simultaneously adv.“同时地”，与 at the same time 同义，故选 B。

question_stem: According to Schwenk's hypothesis as presented in paragraphs 3 and 4, what is theadvantage of a snake’s forked tongue?
choices: tag: A
text: A forked tongue increases the reliability of odor perception because each tine can function as a check to confirm what the other tine senses

tag: B
text: Having a forked tongue, like having two ears or eyes, has the advantage that if one tine becomes disabled the snake can still perceive the environment with the other tine.

tag: C
text: With a forked tongue, one tine is able to sense the odor of a mate, while at the same time the other tine can be used to track a prey animal.

tag: D
text: A forked tongue allows a snake to follow pheromone trails accurately by detecting differences between the two slightly different areas that the left and right tines sense.
answer_key: D
explanation: 题干提问“根据3-4段中提及的 Schwenk 的假说，a snake’s forked tongue 的优点是什么？”。定位第3段第2句为假说，forked tongue 功能（1）同时感知两点的化学刺激；（2）区分气味踪迹差异；（3）增强准确追踪气味踪迹能力；（4）利于捕猎，故选 D。A 的 increases the reliability 未提及，B 的 one tine becomes disabled 未提及，C 的 one tine 交配、one tine 捕猎不符合原文 two tines 同时作业同等功能。

question_stem: According to paragraph 5, snakes and lizards are greatly aided in following odortrails by
choices: tag: A
text: sampling odor trails only when they stop moving

tag: B
text: using their forked tongue to check information from other sensory detectors

tag: C
text: keeping the tines of their tongue widely apart when retrieving odor molecules

tag: D
text: folding the tines of the tongue together when withdrawing it into the mouth
answer_key: C
explanation: 题干提问“snakes and lizards 以何种方式得到了气味踪迹的帮助”。定位第5段（1）对应的第1句：蛇和蜥蜴在回收气味分子时将其舌头张开，spread the tines of their tongue apart = keep the tines of their tongue widely apart，故选 C。A 的 only when they stop moving，B 的 from other sensory detectors，D 的 folding 均未提及。

question_stem: Which of the following is presented in paragraph 5 as evidence supporting the hypothesisthat forked tongues evolved to enhance the ability to follow odor trails?
choices: tag: A
text: The forked tongue adaptation has evolved separately more than once.

tag: B
text: How far snakes and lizards spread the tines of their tongues depends on the type of odor trail they are following.

tag: C
text: There are many more lizard species with forked tongues than without forked tongues.

tag: D
text: In snakes, the chief value of the forked tongue is in finding a mate.
answer_key: A
explanation: 题干提问“以何证据能够支持 forked tongues evolved to enhance the ability to follow odor trails 的假说”。定位第5段（3）对应句：分叉的舌头在不同的爬行动物家族中至少独立进化了两次，表明它们具有适应性。该句提及进化，且通过不止一次的进化体现出其价值（value）所在，即有促进作用，故选 A。BCD 与该题干信息无关且未提及。

question_stem: It can be inferred from paragraph 5 that the tines of the tongue in snakes areconnectedto the nervous system in such a way that
choices: tag: A
text: the tines also serve as the snakes’ means of auditory localization

tag: B
text: information about which signal came from which tine is eventually lost

tag: C
text: a comparison between what one tine picks up and what the other tine picks up is possible

tag: D
text: the two hemispheres of the brain contain exactly the same sensory information
answer_key: C
explanation: 题干提问“以何种方式蛇的 the tines of the tongue 与 the nervous system 连接”。定位第5段（4）对应句：舌头的每个尖齿都与大脑另一侧的一个原子核相连，而两个原子核则跨两个半球相连。类同于哺乳动物和鸟类的听觉系统，是可以通过计算两边的差异而定位，故选 C。A 的 snakes' auditory localization，B 的 eventually lost，D 的 exactly the same 均未提及。

question_stem: Why does the author talk about “gypsy moths” and the “ant nest beetle”?
choices: tag: A
text: To emphasize that the search for mates and prey is often a matter of following odor trails

tag: B
text: To point out that chemosensory perception in snakes and lizards is not very highly developed

tag: C
text: To make the point that snakes and lizards are not unique in having paired chemical receptors

tag: D
text: To show that the work done by the forked tongue is more typically done by special antennae
answer_key: C
explanation: 题干提问“作者为什么谈论 gypsy moths 和 ant nest beetle”。定位第6段 for example 句，为例子，提及例子的目的是为了说明中心句，对应该段第1句：其他物种也进化了成对的化学受体引导个体进行交配或捕食，故选 C。ABD 不能与第6段中心句（第1句）对应。