55. We learn from the text that volunteers in the experiment _____.
(A) were patients with bad coughs
(B) were divided into the three groups
(C) received standard treatments
(D) suffered little side effects

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詳解 (共 1 筆)

#1204313
从第四段首句Ten healthy volunteers(志愿者) were given theobromine, codeine or placebo, a pill that contains no medicine, during the experiment.可知实验中每组人吃一种所给的物品才能看出止咳的效果，故需要三组志愿者。
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