9. 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（B） (E) year, which thus cost the nation $50 billion in lost medical expenses and 这道题C为何不对呢？ | 
