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题库 / Prep2012-CR-64
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?
People in western Africa did not develop staple crops that they stopped cultivating once rice and yams were introduced.
There are no plants native to western Africa that, if domesticated, could serve as staple food crops.
Rice and yams were grown as staple crops by the earliest agricultural societies outside of western Africa.
Kola and okra are better suited to growing conditions in western Africa than domesticated rice and yams are.
Kola and okra were domesticated in western Africa before rice and yams were introduced there.
氣炸，剛剛寫的字都沒了，再寫一遍。
題目難點是a和b的取捨。
看了題目，分析好premise和conclusion，第一個反應就是：在rice引入前，存不存在其他的staple food。如果有，那麼結論就不成立了。所以必要假設是：rice出現前，不存在staple food。
但是這點條件是不夠的 具體看a和b的分析。
a：正確。
注意，假設存在在rice前staple food但是歷史紀錄中沒有record，唯一的解釋是人們再引入rice後沒有再種這些食物。如果是這樣的，那麼conclusion就不成立了，你不可以通過確定rice引入的date去確定西非文明起始點。A，利用negation的技巧，很完美的填補了這個漏洞。
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