Answers: 1-B 2-A 3-D
Quoting from the official explanation:
1-B. The passage suggests that amphibians are “unusually sensitive” because of their permeable skin. Thus, permeable skin must be a relatively unusual characteristic, one not shared by many other animals.
The first sentence of the second paragraph indicates that one third to one half of amphibians “have declined or disappeared.” In order to justify the word “most” in this answer choice, more than half would have had to decline or disappear. Hence, C is wrong.
2-A The last sentence of the first paragraph says that a certain proportion of the species of frogs and toads known to once inhabit an area near Monteverde have disappeared. The language known to indicates that the author is hedging: a total of fifty species are known to live there, but others might exist that have not yet been found
3-D The passage discusses the disappearance of amphibious populations worldwide and hypothesizes that negative effects on ecosystems resulting from human activity may be responsible for these disappearances.