GMAT SC1000 Question No #505

505. 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 costs 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


B is prefect answer. It seems the most of the places costs is typed as cost..otherwise B is correct

Poeple may be confused between B and D but in D 'year that costs' seems year is realted to cost in some way

In all other choices cost is wrong as subject Migraine is singular

Learning

1) singular subject has singular verb..

ANS IS B