单项选择题
In order to change the direction of rotation of a D-Cmotor （） (1) the field leads must be changed (2) the input leads must be changed
A.（1）only B.（2）only C.either（1）or（2） D.neither（1）or（2）
单项选择题 If a small electric motor is immersed in salt water it should be （） (1) washed in fresh water (2) dried in an oven
单项选择题 The unit of electrical power is the （）
单项选择题 In an alternating current electrical system, a low system power factor is a direct sign of （）
