计算机网络是指将多台具有独立功能的计算机，通过通信线路和通信设备连接起来，在网 络软件的支持下实现数据通信和______的计算机系统
If he ____ on tourists for his business,he would have to close his shop.
A. depends
B. will depend
C. depended
D. had depended
He built a telescope ____ he could study the skies in his free time.
It is imperative that you ____ here in time.
A. shall arive
B. must arrive
C. could arrive
D. arrive
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