GRE阅读真题在线练习附答案四

2018-07-27 09:46

来源：新东方在线

作者：

　　Paleontologists'study of the physiognomy of the saber-toothed cat illustrates how scientists extrapolate function from form.Holophoneus, a cat that appeared in North America in the early Oligocene epoch in the Tertiary period of the Cenozoic era, about 38 million years ago, had large upper canines ("saber-teeth") and a downward extension, or flange, formed by the front of the lower mandible. When the mouth was closed, the canines rested just outside the flange, which acted as a guard for these down-pointing teeth; the lower jaw could be opened extremely wide to free the canines for use. Unable to bite like a modern cat, the saber-toothed cat is thought to have used its canines to stab its victims.

　　The evolutionary line of the saber tooth culminated about 2.5 million years ago with the appearance of Smilodon and Megantereon. Smilodon, the larger, was at least as big as the modern African lion (Felis leo) and had upper canines that were sometimes as long as eight inches. Because of its heavily-muscled neck and forequarters, the saber tooth was probably a slow animal that fed on large, slow-moving prey. If that was the case, the extinction of the mammals that constituted the saber tooth's prey probably led to its extinction about 10,000 years ago.

　　The passage is primarily concerned with

　　A.correcting an error of paleontological classification

　　B.examining the evolution of one species of saber-toothed cat

　　C.theorizing about the decline of prehistoric mammals

　　D.discussing the evolutionary significance of certain features of the saber-toothed cat

　　E.analyzing the Oligocene period and its legacy

　　All of the following are true of the Smilodon EXCEPT:

　　A.Smilodon appeared roughly 2.5 million years ago.

　　B.Smilodon could grow larger than the modern African lion.

　　C.Smilodon was smaller than Megantereon.

　　D.Smilodon's neck was heavily muscled.

　　E.Smilodon's canines could grow to a length of more than seven inches.