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问题 选择题

—Why didn’t you answer the phone when I called you last night?

—Sorry, I __________ a bath upstairs.

A．am having

B．have

C．was having

D．had

答案

答案：C

题目分析：考查时态。过去进行时表示在过去某一时刻或某一段时间内进行或发生的动作。这里表示昨天打电话的时候我正在做某事。句意：——昨晚我打电话的时候你为什么不接电话？——对不起，我正在楼上洗澡的。故C正确。

填空题

交流伺服电动机通常分为（）和（）。
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单项选择题

Networks can be interconnected by different devices. In the physical layer, networks can be connected by (11) or hubs, which just move the bits from one network to an identical network. One layer up we find bridges and switches, which operate at data link layer. They can accept (12) ,examine the MAC address, and forward the frames to a different network while doing minor protocol translation in the process. In the network layer, we have routers that can connect two networks. If two networks have (13) network layer, the router may be able to translate between the packer formats. In the transport layer we find transport gateway, which can interface between two transport connections. Finally, in the application layer, application gateways translate message (14) . As an example, gateways between Internet e-mail and X.400 e-mail must (15) the e-mail message and change various header fields.

14（）

A.syntax

B.semantics

C.language

D.format
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