单项选择题
Since fuse elements are made of zinc or any alloy of tin and lead, the melting point of the fuse element must be （）.
A.higher than that of copper B.lower than that of copper C.equal to that of copper D.reached when the conductor it is protecting becomes "white hot"
单项选择题 The most common source of excitation for synchronous motors is a/an （）.
单项选择题 Before reassembling any machinery, you should （）.
单项选择题 Ammeters and voltmeters used in sinusoidal AC power systems indicate which of the following values of the waveforms measured?（）
