Passage 4Questions 76 to 80 are based on the following passage:

题目

Passage 4Questions 76 to 80 are based on the following passage:
Comparatively few fresh-water species of fishes are limited in their distribution to a single river system,yet not many are found on both sides of a high mountain ridge,such as the Rocky Mountains in North America.That is to say,the fishes of the Mississippi Valley are generally different from those of the Pacific slope.While it is a well-known fact that the fish life in no two river systems,even though they empty into the sea on the same side of a divide（分水岭）,is exactly identical,such streams do have many species in common.The principal rivers of the Atlantic slope of the United States,for example,contain several species common to all of them,including the bullhead catfish,the bluegill sunfish,and the largemouth bass.None of these species can endure salt water,so they cannot move from one river system to another.On the other hand,the more northern streams contain species not found in the southern ones,and vice versa.T

答案

C,A,A