往复泵适用于流量较小，扬程要求高，粘度较大的液体。
参考答案：对
In order not to be disturbed, he spent two hours ____ in his study.
A．locking
B．to lock
C．locked
D．being locked
* * 肿块质硬，高低不平，边界不清，腋窝可触及肿块者，多为（）
A.乳癖
B.乳癌
C.乳痨
D.乳疬
E.乳核
