单选题 When the voltage remains constant and the resistance is increased in a series circuit, the flow of current ______. 翻译：在串联电路中，若电压恒定而电阻增大，则电流______。

单选题 The abbreviation of "PF" in the electrotechnics field is equal to ______. 翻译：电工领域中缩写“PF”代表______。

单选题 The relationships of the current and voltage in the following diagrams are ______. (a)in phase (b)lag (c) in phase (a) lead (b)lag (c) in phase (a)in phase (b)lag (c) lead (a)in phase (b) lead (c) lag 翻译：下列图示中电流与电压的关系分别是______。

单选题 When voltage and current developed in an AC circuit reach their peak values at the same time, the power factor is ______. 翻译：当交流电路中电压和电流同时达到峰值时，功率因数______。

单选题 Current flowing in only one direction is called ______. 翻译：仅沿一个方向流动的电流称为______。

单选题 In a three-phase circuit, the phase voltages are ______. 翻译：在三相电路中，各相电压之间______。

单选题 With a purely resistance load, the voltage and current are in phase, giving a power factor of ______. 翻译：对于纯电阻负载，电压与电流同相，功率因数为______。

单选题 The current flowing first in one direction and then in another is called ______ current. 翻译：先沿一个方向流动，然后反向流动的电流称为______。

单选题 Possible phase relationships between voltage and current in an alternating current circuit include which of the following conditions? ①Current and voltage may be in phase; ②Current may lead the voltage; ③ Current may lag the voltage. 翻译：交流电路中电压与电流之间可能的相位关系包括下列哪些？①电流与电压同相；②电流超前电压；③电流滞后电压。