lsat-20-2-17

17. Members of the Amazonian Akabe people commonly take an early-morning drink of a tea made from the leaves of a forest plant. Although they greatly enjoy this drink, at dawn they drink it only in small amounts. Anthropologists hypothesize that since this tea is extraordinarily high in caffeine, the explanation for the Akabe's not drinking more of it at dawn is that high caffeine intake would destroy the surefootedness that their daily tasks require.

Which one of the following, if true, most seriously calls the anthropologists' explanation into question? (A) The drink is full of nutrients otherwise absent from the Akabe diet (B) The Akabe also drink the tea in the evening, after their day's work is done. (C) The leaves used for the tea contain a soluble narcotic. (D) Akabe children are introduced to the tea in only a very weak form. (E) When celebrating, the Akabe drink the tea in large quantities.

我选了b 答案是c 我不能理解。 文章提到含量，并没有说叶子问题啊？ a soluble narcotic 又起道什么作用呢？.

"Anthropologists hypothesize that since this tea is extraordinarily high in caffeine, the explanation for the Akabe's not drinking more of it at dawn is that high caffeine intake would destroy the surefootedness that their daily tasks require. "

C is the answer because: "Narcotic" is something that can induce sleep and stupor. It questions the anthropologists by indicating that  it is this narcotic, rather than caffeine, that destroy the surefootedness of Akabe people.

B is irrelevant.  the hypothesis is concerned with the "surefootedness required for their daily tasks". drinking the tea after all the work done does not explain anything about the daytime when people perform many tasks.