齿轮泵不宜在太低转速使用主要是()。
A.磨损严重
B.噪声太大
C.会发生“气穴现象”
D.容积效率太低
参考答案:D
.—Without your help, we _____ this task on time.
—My pleasure.
A.don’t finish
B.will not finish
C.didn’t finish
D.would not have finished
The consignment certainly does not match the samples()you sent us last month.
A.these
B.-
C.what
D.when