—The company has been performing poorly during the past few years.

—In my view, it needs to _______ its image.

A．hold up

B．take up

C．step up

D．polish up

决定局域网特性的主要技术要素包括 ______、传输介质与介质访问控制方法。

A．所使用的协议

B．网络拓扑结构

C．数据传输环境

D．主机的时钟频率