间歇强化的方式不包括( )。
A．定时制
B．定编制
C．不定时制
D．不定率制
参考答案：B
The ______ look on the student’s face suggested that your ______ question made him ______.
A．puzzling; puzzled; puzzled
B．puzzling; puzzling; puzzled
C．puzzled; puzzled; puzzling
D．puzzled; puzzling; puzzled
方向保护是反映电流与电压之间的相位角变化。（）
