TOEFL Reading Passage 1

1. One of the most intriguing physical characteristics of snakes is their forked tongues. While this trait is also shared by some types of lizards, all snake species exhibit split tongues, which usually have a more pronounced fork than those of lizards. Any observer of snakes has no doubt noticed that they often stick their tongues out of their mouths, flick them up and down in the air, and then retract them. In fact, due to a slight indentation in the upper jaw, many species can protrude their tongues without even opening their mouths.
2. The explanation for this behavior remained unknown for centuries, giving rise to many folk superstitions. For example, the forked tongue has become synonymous with deceit, from the idea that two separate tongues would enable a creature to voice two contrasting ideas at the same time. Another popular misconception is that snakes sting other animals with their tongues. Recently, though, scientists uncovered the truth about the forked tongue, and its actual use is much less sinister.
3. Snakes differ greatly from humans on a sensory level. On the one hand, their eyesight is poor and they lack outer ears so they cannot hear with much volume or clarity, but, on the other, some have the ability to "see" and hunt in the dark by sensing the body heat of their prey. In addition, snakes have a method of smelling that is peculiar in that it is actually performed by the tongue rather than by the nostrils and nasal cavities, which in fact undertake other functions, such as breathing. When a snake flicks its tongue around in the air, it is actually snaring chemical particles, which can be thought of as odors. Next, the snake brings its tongue back in and places it against the roof of its mouth, where there are two small openings that correspond to the two tips of the forked tongue. These make up the snake's Jacobson's organ, a kind of chemoreceptor that analyzes the chemical odors on the tongue and sends this information to the snake's brain.
4. This technique for "smelling" the surrounding environment is truly unique, but even more amazing is the reason why the snake's tongue is forked. By spreading the tips apart when the tongue is flicked out, each samples chemical particles from a slightly different position in the air and brings them back to the Jacobson's organ.The organ then determines which tip was exposed to a larger amount of the particles in question, and this data tells the snake where the source of the odor can be found. In other words, if the tongue's right tip contains more of the particles, such as those of an animal's chemical odor, the snake knows that to find the animal it must travel to the right, not to the left.
5. Obviously, the ability of snakes to pursue scents in this fashion is very useful in hunting, It has been proven to be quite accurate, allowing them to pick up the trail of rodents and other prey even though the animal itself may be a great distance away. Similarly, if the odor the snake perceives belongs to a predator, it is able to adjust its course to steer clear of the danger, Another suggested use of snakes' sense of smell is that it aids them in ascertaining the locations of communal dens*, where snakes reside in groups during the winter months.

单选题 The word pronounced in the passage is closest in meaning to
A. controlled.
B. obvious.
C. evolved.
D. useful.

单选题 According to Paragraph 1, many snake species have the ability to
A. stick out their tongues while their mouths are shut.
B. imitate the behavior of lizards.
C. bring prey into their mouths with their tongues.
D. retract the lips from their jaws.

单选题 In Paragraph 2, why does the author list folk superstitions?
A. To suggest that they inhibited true knowledge about snakes from progressing.
B. To emphasize that snakes are considered dangerous by most people.
C. To explain the origins of scientific research into snakes' tongues.
D. To describe the mystery that has been associated with snakes' irregular tongues.

单选题 According to Paragraph 3, how do the senses of snakes differ from those of humans?
A. Snakes use their nostrils and nasal cavities when smelling.
B. Snakes have less developed hearing abilities than humans.
C. Snakes' eyesight is better at night than during the day.
D. Snakes' sensitivity to heat is less than that of humans.

单选题 5, The word snaring in the passage is closest in meaning to
A. testing.
B. keeping.
C. forming.
D. catching.

单选题 The word These in the passage refers to
A. particles.
B. openings.
C. tips.
D. odors.

单选题 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.
A. Snakes have an unusual method of smelling which is similar to the way other animals breathe.
B. As well as being used for smelling, the nostrils and nasal cavities also serve the additional function of allowing the snake to breathe.
C. Uniquely, a snake's tongue is what helps it to pick up scents, and its nostril or nasal cavity is for other tasks.
D. As well as having peculiar tongues, snakes also have distinctive nostrils and nasal cavities.

单选题 According to Paragraph 4, what is the function of the Jacobson's organ in snakes?
A. To assist in the search for chemical particles in the air.
B. To enable the tongue's fork to be spread more widely.
C. To utilize the snake's trained sense of direction.
D. To compare the sensory input of the two tongue tips.

单选题 The word perceives in the passage is closest in meaning to
A. imitates.
B. discharges.
C. notices.
D. carries.

单选题 All of the following are mentioned in Paragraph 5 and Paragraph 6 as ways in which snakes use their tongues EXCEPT
A. avoiding animals that may pose a threat to them.
B. finding a snake of the opposite sex in order to reproduce.
C. following other snakes during cooperative hunts.
D. determining the location of potential food sources.

单选题 What can be inferred from Paragraph 6 about the pheromones of female snakes?
A. They are produced year round.
B. They are species specific.
C. They are only detectable by male snakes.
D. They are the strongest chemical odors.

单选题 Look at the four squares [■] that indicate where the following sentence could be added to the passage.
Young snakes especially may rely on their tongues and Jacobson's organs to follow the scents left by adults on their way to these hibernation spots.
Where would the sentence best fit?
Click on a square [■] to add the sentence to the passage.
A. Square Ａ.
B. Square Ｂ.
C. Square Ｃ.
D. Square Ｄ.

填空题 Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
The forked tongues of snakes have puzzled people for centuries, and their true function has only recently been discovered.
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A. The only animals other than snakes that possess forked tongues are lizards, though there are some important differences between the two.
B. Despite what superstitions may suggest, snakes actually use their tongues to smell their surroundings.
C. The fork in the tongue enables the snake to sample odors from two different places, and its Jacobson's organ then determines where the smell is coming from.
D. The sensitivity of snakes' Jacobson's organ makes it possible for them to track animals even when a great distance separates them.
E. Scientists believe snakes use their tongues for hunting and navigation, but their primary role most likely deals with mating.

F. Snakes use the olfactory sensors in their tongues to ensure that they do not stray too far while traveling in groups.