He told me to ________, for he wanted to stay for a while all by himself.

A．leave him behind

B．leave him out

C．leave him alone

D．leave him off

在构成电机的材料中，最薄弱、在很大程度上也是决定电动机使用寿命的材料是（）材料。

A．导电

B．铁磁

C．绝缘

D．其他非电工