16. Migraine, the most debilitating common form of headache, afflicts perhaps 18 million Americans, who collectively lose 64 million workdays a year, and they cost the nation $50 billion in medical expenses and lost work time.
(A) year, and they cost the nation $50 billion in medical expenses and lost
(B) year and thus cost the nation $50 billion in medical expenses and lost
(C) year, so as to cost the nation $50 billion in medical expenses and lost
(D) year that costs the nation $50 billion in lost medical expenses and
(E) year, which thus cost the nation $50 billion in lost medical expenses and请问thus是否可指代前面一句话的内容，那么其后的谓语动词用单数还是复数？而且这道题中，cost为何不用costs呢?作者: finnlijing 时间: 2011-11-25 06:36
thus一般与and连用,表因果关系,而这里lose and thus cost两个V并列做who的谓语,因为who指代americans,所以用复数作者: genius1824 时间: 2011-11-26 06:31
cost 的主语是“Migraine",在migraine之后的“the most debilitating common form of headache, afflicts perhaps 18 million Americans" 都是插入语，修饰migraine的。作者: 87338618 时间: 2011-11-29 21:06
