The children all turned _____ the famous actress as she entered the classroom. [ ]

A. looked at

B. to look at

C. to looking at

D. look at

抽汽器的作用是抽出凝汽器中（）。

A、空气

B、蒸汽

C、蒸汽和空气混合物

D、空气和不凝结气体