The conclusion is: Members of the tribe drink the tea in small quantities because the tea contains high levels of caffeine.
(A) The drink is full of nutrients otherwise absent from the Akabe diet.
- This doesn't impact the conclusion. Sure, the tea is full of nutrients but how does that explain the small amounts in which the members take the tea. If let's say that the only way the nutrients in tea are effective is when the tea is sipped in small amounts, then perhaps this answer would have been worth considering.
(B) The Akabe also drink the tea in the evening, after their day’s work is done.
- This strengthens the argument. The anthropologists believe that the reduced intake is to make sure that the members are able to do their daily work. If they are drinking the tea after the day's work is done then it means that the high caffeine does interfere with their work.
(C) The leaves used for the tea contain a soluble narcotic.
- C is the answer because C presents an alternative reason to the anthropologist's hypothesis. It is not the caffeine but the narcotic that is the reason for drinking the tea in small amounts. The argument is about the reason why the members of the tribe drink the tea in small amounts. The anthropologists believe it is the high caffeine content but we can the weaken that argument by saying - no, it is not, it is actually the presence of a narcotic element in the tea which is why the tea is sipped in small amounts.
(D) Akabe children are introduced to the tea in only a very weak form.
- This is irrelevant.
(E) When celebrating, the Akabe drink the tea in large quantities
- Again, irrelevant. How does the impact the conclusion?