The doctor informed his patient that the drug was very______and can have unpleasant side effects.
【正确答案】 A
【答案解析】各项的意思是:potent(药等)效力大的;强有力的;efficient有能力的;效率高的;intricate错综复杂的;fragile易碎的;虚弱的。根据句意判断,答案是A。