发球台标
参考答案：
在发球台上确定发球区域的标识物，以两个发球台前面和两侧所限定的纵深为两球杆长度的长方形区域。
Only when something gets lost _____________.
A．can you realize how important it is to you
B．how important you can realize it is to you
C．you can realize how important it is to you
D．can you realize how important is it to you
集线器、网桥、交换机、路由器分别应用在什么场合？它们之间有何区别？
