electrical fields) clustered at the tip of the spiny anteater's snout. The researchers made this discovery by exposing small areas of (5) the snout to extremely weak electrical fields and recording the transmission of resulting nervous activity to the brain. While it is true that tactile receptors, another kind of sensory organ on the anteater's snout, can also respond to electrical stimuli, such receptors do so only in response to ( 10) electrical field strengths about 1,000 times greater than those known to excite electroreceptors.

　　Having discovered the electroreceptors, researchers are now investigating how anteaters utilize such a sophisticated sensory system. In one behavioral experiment, researchers (15) successfully trained an anteater to distinguish between two troughs of water, one with a weak electrical field and the other with none. Such evidence is consistent with researchers' hypothesis that anteaters use electroreceptors to detect electrical signals given off by prey; however, ( 20) researchers as yet have been unable to detect electrical signals emanating from termite mounds, where the favorite food of anteaters live. Still, researchers have observed anteaters breaking into a nest of ants at an oblique angle and quickly locating nesting chambers. This ability quickly (25) to locate unseen prey suggests, according to the researchers, that the anteaters were using their electroreceptors to locate the nesting chambers.

　　1. According to the passage, which of the following is a characteristic that distinguishes electroreceptors from tactile receptors?

　　(A) The manner in which electroreceptors respond to electrical stimuli

　　(B) The tendency of electroreceptors to be found in clusters

　　(C) The unusual locations in which electroreceptors are found in most species.

　   (D) The amount of electrical stimulation required to excite electroreceptors

　　(E) The amount of nervous activity transmitted to the brain by electroreceptors when they are excited

　　2. Which of the following can be inferred about the experiment described in the first paragraph?

　　(A) Researchers had difficulty verifying the existence of electroreceptors in the anteater because electroreceptors respond to such a narrow range of electrical field strengths.

　　(B) Researchers found that the level of nervous activity in the anteater's brain increased dramatically as the strength of the electrical stimulus was increased.

　　(C) Researchers found that some areas of the anteater's snout were not sensitive to a weak electrical stimulus.

　　(D) Researchers found that the anteater's tactile receptors were more easily excited by a strong electrical stimulus than were the electro receptors……

　　(E) Researchers tested small areas of the anteater's snout in order to ensure that only electroreceptors were responding to the stimulus.

　　3. The author of the passage most probably discusses the function of tactile receptors (lines 7-11) in order to

　　(A) eliminate and alternative explanation of anteaters' response to electrical stimuli

　　(B) highlight a type of sensory organ that has a function identical to that of electroreceptors

　　(C) point out a serious complication in the research on electroreceptors in anteaters.

　　(D) suggest that tactile receptors assist electroreceptors in the detection of electrical signals.

　　(E) introduce a factor that was not addressed in the research on electroreceptors in anteaters.