单项选择题
Current changing in direction and rising and falling in value is （）.
A.AC B.DC C.generator D.fresh water generator
单项选择题 The output voltage of a three-phase alternator is regulated by the （）.
单项选择题 To repair a small electrical motor that has been submerged in saltwater, you should （）.
单项选择题 A fuse that blows often should be replaced only with a fuse of （）.
