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

答案是B,我想问问在这题中到底是18 million americans还是64 million workdays 做cost的主语，

在请各位帮忙分析一下个选项的错误，我选的E

句子的核心部分是migraine,afflicts perhaps 18 million americans

E的错误在:

1.which 如果在此做定语从句的关系代词,其先行词就应该是前面的year,那么就改变了句子的意思.

2.which是如果做定语从句的关系代词,在从句中做主语,那么所指代先行词就是year--[sing],那么cost就要加S.

3.who collectively lose 64 million workdays year, which thus cost the nation $50 billion in lost medical expenses and work time.

改变句子的意思了.以which为关系代词,句子就是"工作年花费.."

4.还有一处改变句子意思.

正确选项:in medical expenses and lost work time.

此时的lost是形容词与medical平行.指的是浪费的工作时间.

原意就是"在医疗成本以及浪费的工作时间"

E的意思"在浪费的医疗成本和时间".

一点看法.希望对你有用

migraine, the most debilitating common form of headache, afflicts perhaps 18 million americans, who collectively lose 64 million workdays year and thus cost the nation $50 billion in medical expenses and lost  work time

这是一个主从关系的句子,主句是migraine, the most debilitating common form of headache, afflicts perhaps 18 million Americans, 主句的成分分析是主语:Migraine, 谓语 afflicts 宾语 18 million Americans,从句是一个由who引导的定语从句,其中Americans是先行词,who作为关系代词在从句中做主语,也就是说"美国人完全失去了...."