Edison is said to _____the first telephone. [ ]
A. find
B. discover
C. invent
D. found
答案:C
叉手自冒心
机油泵常见的形式有()。
A.柱塞式与膜片式
B.齿轮式与膜片式
C.转子式与活塞式
D.转子式与齿轮式