排水阀在蒸汽管网中的作用包括（）。
A.排出空气
B.阻止蒸汽逸漏
C.调节气流
D.排放凝结水
E.阻止水锤
参考答案：A, B, D, E
— I saw Tony at the party. But he didn't speak to me _____ evening.
— Maybe he didn't see you. [ ]
A. all
B. every
C. either
D. another
