The poor boy couldn't work the problem out. He wasn't ____ clever.

A．that

B．much

C．enough

D．too

引起下列疾病的病毒能在体内长期存活的是（）。

A.沙眼和癣病

B.单纯疱疹和水痘

C.天花和疖

D.猩红热和疣