When Henry arrived home after a hard day at work, his wife was slept .

A．his wife was sleeping

B．his wife slept

C．his wife has slept

D．his wife has been sleeping

采用CSMA/CD介质访问控制方法的局域网适用于办公自动化环境。这类局域网表现出较好的吞吐率与延迟特性是在（）网络通信负荷情况下。

A．较高

B．较低

C．中等

D．不限定