迷惑的一道关于并列形式的例题

寂寞的自由

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. B
(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
正确答案是B，请大家给些思路和建议，谢谢

寂寞的自由

D）和E）的THAT 与WHICH应该改变成为WHEN，来修饰YEAR才对。A）的THEY和原句中的WHO重复矛盾。

这个是我对这个题的排除方法，请大家多给些建议，谢谢

dreadpower

A：they无指代
   C：so as to连用必错，讨论过
   D：that修饰year 错
        in lost medical expenses and work time改变句子意思了
   E：which修饰year 错
        in lost medical expenses and work time改变句子意思了

    另外：sth cost sb some money

snow_mountain

这里不是平行结构。 A 中them 逻辑指代 americans， 意思上说不通。  

so as to 结构用在这里不对。

D E， 中that 和which 从句都不对。它们不能修饰 “afflict ... Americans” 这个动作。

snow_mountain

以下是引用dreadpower在2004-1-14 12:45:00的发言：
    C：so as to连用必错，讨论过
   

     

为什么 so as to 连用必错，能否解释一下，或者提供链接？ 谢谢。