阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用

括号中单词的正确形式填空，并将答案填写在1-5空格中。

     Now people think that 1            is very important to communicate with others, so radio, telephone

and television are widely used all over the world. When you turn on the radio, you can listen. But when

you use telephone, not only can you listen to others but also you can chat 2             them. 3            ,

you can't see the other one at all. Television is even 4            (good) than both of them. People can

watch TV and listen to it, but you 5             (can) take part in what you see. Perhaps in the near future,

another new kind of phone will come into wider uses in our daily life.

下列哪项不属于NetWare操作系统的三种容错技术？

A．UPS监控

B．文件服务器监控

C．事物跟踪系统

D．三级容错机制