请教gwd 一道逻辑题

zhaozihan

11-22 Whales originated in the freshwater lakes and rivers of ancient Asia about sixty million years ago .Not until about ten million years later did species of whales develop specialized kidneys enabling them to drink salt water .Although fossil evidence shows that some early whale species that lacked such kidneys sometimes swam in the Earth's saltwater oceans,these species must have had to return frequently to freshwater rivers to drink .

加强题目

key: Fossils of whale species dating from between sixty million and fifty million years ago will not be found on continents that were at the time separated from ancient Asia by wide expanses of ocean  如何理解 谢谢

xfi883

挺像假设题的！

原文大意：

鲸鱼起源于6千万年前的古亚洲内陆淡水之中。

直到5千万年前，鲸鱼才能游入“远”海，

因为，即使6千万到5千万年前，鲸鱼偶尔游入“近”海，也必须马上回到内陆淡水中。

如果要加强，就要加强前提。答案应该是：6千万到5千万年前，没有鲸鱼能游到“远”海。

那么正确答案的意思恰好是：在6千万到5千万年前，没有在“被大海分割的，与古亚洲大陆隔海相望的，大陆上”发现鲸鱼化石。也就是说，除了古亚洲大陆，其他大陆都没有鲸鱼。

[此贴子已经被作者于2009-6-29 10:46:28编辑过]