单项选择题
The part of a fuse that melts and opens the circuit is made of （）.
A.copper and antimony B.steel and babbitt C.aluminum or beryllium alloy D.zinc or an alloy of tin and lead
单项选择题 Time delayed or delayed action-type fuses are designed to （）.
单项选择题 Which of the following statements is true concerning all three-phase alternators?（）
单项选择题 The function of damper windings in a synchronous motor is to （）.
