Insect-eating bats rely heavily on echolocation, a method of sensory p

The first paragraph of the passage explains that bats use echolocation and broadly describes how echolocation works. The second paragraph explores the nuances of echolocation in bats, with a particular emphasis on the importance of noseleaves in certain bat species.

(A) A particular process – echolocation – is mentioned in the first paragraph. However, the second paragraph never discounts the complexity of this process. Instead, it expounds upon the complexity of this process.

(B) A biological system – echolocation – is discussed in the first paragraph. However, no debate over echolocation is mention in the second paragraph or anywhere else in the passage.

(C) CORRECT. The first paragraph does introduce a method: echolocation. The second paragraph then offers insight into, or illuminates, certain complexities of echolocation, such as how bats are able to utilize their noseleaves to emit differing frequencies.

(D) The first paragraph does not establish a hypothesis; instead, the first paragraph simply explains, in broad terms, the method of echolocation in bats.

(E) The second paragraph does describe the function of a particular physical feature: noseleaves. However, this feature is never mentioned in the first paragraph.

According to the passage, the purpose of the noseleaves is to help bats “perform difficult tasks, such as locating prey while avoiding obstacles.” The noseleaves do so by allowing bats to emit differing frequencies of sound in different directions. These sound waves “bounce off objects and surfaces and then return to the animals’ ears,” providing the bats with vital information about their surroundings. To weaken the conclusion about the purpose of noseleaves, we must demonstrate that they do not necessarily aid bats in accessing this vital information.

(A) CORRECT. For the noseleaves to contribute to the bats’ understanding of their surroundings, the bats must be able to interpret the information provided by the different frequencies of sound. According to this choice, the bats are emitting at various frequencies, but are “receiving” only a small percentage of what they emit. This idea weakens the conclusion that the noseleaves, by allowing bats to emit a greater range of frequencies, contribute to an enhanced awareness of the immediate environment.

(B) The fact that many bats emit sounds through their mouths does not weaken the conclusion concerning the purpose of noseleaves for those bats that do possess this distinctive feature.

(C) Dolphins live in an environment that is completely different from that of bats. Thus, it is not possible to draw definitive conclusions about the noseleaves of bats simply because dolphins lack such a feature.

(D) For several reasons, the fact that some bats rely on sight and smell does not undermine the conclusion about noseleaves. First, we do not know which bats act in this manner or whether these bats even possess noseleaves. Second, “some” is an ambiguous term; it could refer to a few species of bats rather than a large number. Finally, the passage implies that echolocation is most useful while bats are in motion and their prey is also in motion (echolocation allows bats to “snatch insects out of the air”). It is very possible that bats have alternative strategies when their sources of food are stationary.

(E) The limited range of echolocation does not undermine the purpose of the noseleaves. It is very possible that many “difficult” tasks must be accomplished within a short distance from where bats emit their signals.

On the GMAT, the answer to an inference question must be directly supported by evidence from the text. As always, be sure to pay particular attention to the precise words used in the answer choices and how these words relate to the information presented in the passage.

(A) The second paragraph of the passage states that “lower frequency sounds are spread more vertically, while higher frequency sounds emit more horizontally” (lines 37-40). Thus, sound waves are emitted in a range of directions rather than just vertically and horizontally.

(B) The second paragraph of the passage relates the importance that the grooves found on noseleaves play in echolocation. No information is given concerning the role that the spikes play. Because we have no information about the spikes, we cannot infer anything about their role during echolocation.

(C) The passage does highlight the importance of echolocation, but it neither contrasts this ability with bats’ sense of sight nor even mentions the sense of sight. Thus, this answer choice is outside the scope of the passage.

(D) The first paragraph of the passage states that bats use high-frequency sound waves “since high-frequency waves do not diffract, or bend, extensively” (lines 11-13). Thus, it can be inferred that low-frequency sound waves diffract more than high-frequency sound waves.

(E) CORRECT. The first paragraph of the passage states that “while using echolocation, these bats emit a series of short, high-frequency sounds from their mouths or nostrils” (lines 6-8). Then, the first sentence of the second paragraph indicates that “bats emit slightly different frequencies in differing situations.” Taken together, these statements confirm that bats emit only high frequencies during echolocation. The variations in the sound waves' frequencies are slight, so that even the "lower frequency sounds" mentioned in lines 37-38 are within the range considered high-frequency.