单选题 _______ is used to measure the voltage

单选题 ______ is used to measure the current.

单选题 Current following in only one direction is called _____.

单选题 _____ is used to change the frequency of the alternating current

单选题 The unit of electrical current is the _____

单选题 The unit of electrical resistance is the _______

单选题 In China, the rated frequency of the electrical power system is 50 ______.

单选题 _____ is used to produce electric power