In my opinion,older people should________their own friends rather than become emotionally

dependent on their children.[ ]

A. spy  

B. seek  

C. serve  

D. stress

下列哪一项不是网络卡在物理层实现的功能

A．对发送信号的传输驱动

B．对进来信号的侦听与接收

C．对信号进行差错校验

D．对数据的缓存