信息资源与服务的提供者，我们叫做（）。
A.便携机
B.主机
C.客户机
D.服务器
参考答案：D
7. There is no ___________ in trying to talk him into joining us. He enjoys being alone.
A．doubt
B．wonder
C．hope
D．Point
在一定的地域内______与______构成的统一整体就是生态系统．在这个系统中，物质和能量沿着______和______流动．
___________ in trying to talk him into joining us. He enjoys being alone.