题目内容

I turned the bed over. A large brown envelope is __1__ "DON NOT THROW AWAY" I open it. More papers. I __2__ the contents onto the floor. They are old family photographs, letters, greeting cards and __3__ from us to her. There are comics __4__ from newspapers and magazines. Every single item in this envelope has passed from our hands to __5__, These are all things that we give her. Suddenly, I feel very __6__.

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三相对称电路是指( )。

A. 电源对称电路
B. 负载对称的电路
C. 电源和负载均对称的电路
D. 三相电压对称电路

三相负载对称是指( )。

A. 各阻抗相等
B. 阻抗角相等
C. 各阻抗值相等,且阻抗角相等
D. 电阻值相等,阻抗角相等

在低压三相四线制回路中,要求中性线不能( )。

A. 装设电流互感器
B. 装设电表
C. 安装漏电保护器
D. 安装熔断器

对称三相电路负载为三角形连接时,线电流比对应的相电流( )。

A. 同相位
B. 超前30°
C. 滞后30°
D. 滞后60°

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