铅元素的加入是为了改善黄铜的（）性能。
A、焊接
B、耐磨
C、导热
D、切削
参考答案：B
— Oh, dear! Who's broken my glasses?
— _____ he _____ I. It was your cat. [ ]
A. Either, or
B. Neither, nor
C. Both, and
D. Not only, but also
离心泵的基本构造，由哪些主要零部件组成？
