The question______new measures should be taken to control the terrible air pollution is______puzzles scientists a lot.

A．that; what

B．which; that

C．what; what

D．which; that

加热时牛乳质量的一般变化：（）。

A、形成薄膜，

B、棕色化，

C、白色化，

D、蒸煮味。