It’s uncertain side effect the medicine will bring about , although about two thousand patients have taken it ．
A. that
B. what
C. how
D. whether
网友回答
A. that
(答案→)B. what
C. how
D. whether
解析：考查宾语从句，it 做形式宾语，真正的宾语是后面的从句，而从句中bring about后缺少宾语，故用what,what又做定语修饰side effect，所以选B。