电液伺服阀的滑阀是（）机能。
A、O型
B、I1型
C、Y型
D、M型
参考答案：A
纯天然橡胶硫化后的抗张强度为（）MPa。
A.5～10；
B.11～16；
C.17～29；
D.30～40。
You________all those clothes!We have a washing machine to do that sort of thing.[ ]
A. needn't have washed
B. shouldn't have washed
C. must not have washed
D. can not have washed
