扫描二维码，直接登录
题库 / Prep2012-CR-73
The Earth's rivers constantly carry dissolved salts into its oceans. Clearly, therefore, by taking the resulting increase in salt levels in the oceans over the past hundred years and then determining how many centuries of such increases it would have taken the oceans to reach current salt levels from a hypothetical initial salt-free state, the maximum age of the Earth's oceans can be accurately estimated.
Which of the following is an assumption on which the argument depends?
The quantities of dissolved salts deposited by rivers in the Earth's oceans have not been unusually large during the past hundred years.
At any given time, all the Earth's rivers have about the same salt levels.
There are salts that leach into the Earth's oceans directly from the ocean floor.
There is no method superior to that based on salt levels for estimating the maximum age of the Earth's oceans.
None of the salts carried into the Earth's oceans by rivers are used up by biological activity in the oceans.
background: 河流会把溶解了的盐带入海洋中。
所以只要决定1）现在海洋中的盐份增加的水平；2）要花多少年才能让海洋中的盐从零增长到现在的水平。就可以决定出地球上海洋的最大年龄。问assume
choice a, 在过去的几百年间，河流里溶解的盐的水量不会特别高。correct，取非，如果在某一段时间内河流内含盐量很高，那么计算出来的海洋年龄是偏小的
choice b, 在任何时间，河流的含盐量都是一样的。incorrect，并不要求每一条河流的含盐都一样，只要保证每一年的总和都差不多
choice c, 会有盐从海床中直接流入海洋。weaken the conclusion，说明盐不只从河流一个渠道进入海洋
choice e, 从河流中带入海洋的盐没有一点点被海洋中的生物活动所消耗掉。incorrect，只要是消耗掉微量的盐，还是可以准确测量出海洋的年纪的
谢谢！
登录 或 注册 后可以参加讨论