战略管理系统是由（）三者紧密结合构成的。
A.主体
B.客体
C.环境
D.制度
参考答案：A, B, C
计算机网络采用层次结构，各层之间互相 【2】 。
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
