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问题 多项选择题

在乙烯制冷系统与乙烯精馏塔组成的开式热泵系统中，乙烯机停车之前的操作有（）。

A．停止乙烯精馏塔回流

B．降低各换热器液面

C．停乙烯产品采出

D．乙烯机降低负荷

答案

参考答案：B, C, D

单项选择题

In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.

To a router, a flow is a (1) of packets that share the same characterstics, such as traveling the same (2) , using the same (3) , having the same kind of security, and so on. A router that supports the handling of flow labels has a (4) table. The table has an entry for each Active flow label; each entry defines the (5) required by the corresponding flow label.

1（）

A．sequence

B．stream

C．Queues

D．flow
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多项选择题

单位和个人都可以采用的结算方式是()

A.支票

B.银行本票

C.银行汇票

D.商业汇票
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