Scientists have long known that the soft surface of the bill of the platypus is perforated with openings that contain sensitive nerve endings. Only recently, however, have biologists concluded on the basis of new evidence that the animal uses its bill to locate its prey while underwater, a conclusion suggested by the bill. But Bohringer’s investigations did not explain how the animal locates its prey at a distance.
Scheich’s neurophysiological studies contribute to solving this mystery. His initial work showed that when a platypus feeds, it swims along steadily wagging its bill from side to side until prey is encountered. It thereupon switches to searching behavior, characterized by erratic movements of the bill over a small area at the bottom reasonable to assume that all the invertebrates on which the platypus feeds must produce electric fields.
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Find what must be true based on what the passage or stimulus states.
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Answers that are plausible or likely but not actually guaranteed by the text.
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Keep only the choice the statements fully support — eliminate anything that requires an extra assumption.
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