21. One method of dating the emergence of species is to compare the genetic material of related species. Scientists theorize that the more genetically similar two species are to each other, the more recently they diverged from a common ancestor. After comparing genetic material from giant pandas, red pandas, raccoons, coatis, and all seven bear species, scientists concluded that bears and raccoons diverged 30 to 50 million years ago. They further concluded that red pandas separated from the ancestor of today’s raccoons and coatis a few million years later, some 10 million years before giant pandas diverged from the other bears. Which one of the following can be properly inferred from the passage? (A) Giant pandas and red pandas are more closely related than scientists originally thought they were. 这可没提到 (B) Scientists now count the giant panda as the eighth species of bear. (C) It is possible to determine, within a margin of just a few years, the timing of divergence of various species. (D) Scientists have found that giant pandas are more similar genetically to bears than to raccoons. Red pandas(raccoons)---10 million years---giant pandas(bears); Bears---30 or 50 million years---raccoons(D) (E) There is substantial consensus among scientists that giant pandas and red pandas are equally related to raccoons. manhattan的解释:http://www.manhattanlsat.com/forums/q21-one-method-of-dating-the-emergence-of-species-t3869.html
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