It is 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： 考查连词。What“什么样的”做定语，限定side effect。“虽然两千多病人使用过这种药，但是会带来什么样的副作用还不确定。”