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

焊丝送进和电弧移动都由专门的焊接装置自动完成的埋弧焊类型是（）。

A.压焊

B.半自动埋弧焊

C.自动埋弧焊