新东方逻辑分册 综合练习 88题

Agricultural societies cannot exist without staple crops. Several food plants,such as kola and okara, are known to have been demesticated in western africa, but they are all supplemental ,not staple,foods.All the recorded staple crops grown in western africa were introduced from elsewhere,beginning, at some unknow date, with rice and yams. Therefore,discovering when rice and yams were introduced into western africa would establish the earliest date at which agricultual societies could have arisen there.

which of the following is an assumption on which the argument depends?

a. people in western africa did not develop staple crops that they stopped cultivating once rice and yams were introduced.

b. there are no plants native to african that, if domesticated,could serve as staple food crops.

c. rice and yams were grown as staple crops by the earliest agricultural societies outside of western africa.

d.kola and okra are better suited to growing conditions in western africa than demesticated rice and yams are,

e.kola and okra were demesticated in western africa before rice and yams were introduced there.

这道题答案是a, why not b? a 选项中“staple crops that they stopped cultivating once rice and yams were introduced”说明了rice 和yams被引进之前，本地就有staple crops，既然如此，只确定rice,yams被引进的时间怎么就能推出the earliest date呢？？

can somebody help me out?

没有人来么。。。。。。

自己顶一下。。

A是在讲:在rice来之前是没有其它的stable crop的.

好象不是你那么理解的.

恩．．偶觉得应该也是这个意思，但是光看单独这句话就是觉得还是有问题

＂that they stopped cultivating ＂是修饰前面的staple crops的么？昏头了．．

哦,你说这个呀.这就是你想的那个,以前有别的stable crop, 后来不种了.改种大米.

ah!!

finally got it!　呼．．．．．松口气．．

gmaht & wycg

thank u so much u guys