弱弱地问:白勇语法11-07.请NN指教

gedn01

7.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 expense and lost work time

b. year and thus cost the nation $50 billion in medical expense and lost

c.year,so as to cost the nation $50 billion in medical expense and lost

答案选b,它说c项随意添加so as to 表示动作lose 64 million workdays a year的结果,逻辑意思不合理.

这里我想问who collectively lose 64 million workdays a year 当作18 million Americans的定语,so as to 可以跨过它去表示afflicts perhaps 18 million Americans的结果的吧.这样逻辑意思是合理的吧

joywu1221

so as to 在GMAT就没对过，是wordy的用法。