gwd-9-40 ??

Q40:

Agricultural societies cannot exist without staple crops.  Several food plants, such as kola and okra, are known to have been domesticated 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 unknown date, with rice and yams.  Therefore, discovering when rice and yams were introduced into western Africa would establish the earliest date at which agricultural societies could have arisen there.

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

1. People in western Africa did not develop staple crops that they stopped cultivating once rice and yams were introduced.

2. There are no plants native to western Africa that, if domesticated, could serve as staple food crops.

3. Rice and yams were grown as staple crops by the earliest agricultural societies outside of western Africa.

4. Kola and okra are better suited to growing conditions in western Africa than domesticated rice and yams are.

5. Kola and okra were domesticated in western Africa before rice and yams were introduced there.

   Answer: 

A.People in western Africa did not develop staple crops that they stopped cultivating once rice and yams were introduced

正确选项A， 怎么看起来有点费解阿？？其中的定语从句“that they stopped cultivating” 是什么意思？？

这样就证明rice and yams were是第一种被种植的staple啊。
that they stopped cultivating是说停止种植这些农作物。 如果以前有种其他的staple，等rice and yams来了后才停种，就不能引出最后的结论了。

呵呵，明白了。

 怎么脑袋又有点打结了似的。。。。。。