密封油的作用是（）。
A.密封氢气
B.润滑
C.冷却
D.密封二氧化碳
参考答案：A, B, C
（）Very well, thank you. And you?
A.Good night.
B.How ar eyou?
C.How do you do?
D.How do you like Chinese?
肩带
