我选了E,根据结论 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.如果A正确,那么如何证明结论的前半部分? 必须回到淡水来喝水不等于不能在盐水中生存,也许可以生存,只是经常要到某地方喝水.或许只要喝上一口,就能象骆驼一样在沙漠生存好几个月.
看E, the freshwater lakes and rivers in which whales originated were gradually invaded by salt water.这样白鲸就能自如地从盐水return frequently to freshwater rivers to drink.也更好地支持了 about ten million years later did species of whales develop specialized kidneys enabling them to drink salt water. 因为,器官的进化确实是演化gradually
[此贴子已经被作者于2006-12-10 11:23:22编辑过] |