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问题 选择题

下列变化过程中，ΔS＜0的是 [ ]

A．氯化钠溶于水中 　

B．NH3(g)和HCl(g)反应生成NH4Cl（s）

C．干冰的升华 　

D．CaCO3(S)分解为CaO(s)和CO2(g)

答案

答案：B

单项选择题

A transport layer protocol usually has several responsibilities．One is to create a process-to-process communication；UDP uses (1) numbers to accomplish this．Another responsibility is to provide control mechanisms at the transport level．UDP does this task at a very minimal level．There is no flow control mechanism and there is no(2) for received packet．UDP, however, does provide error control to some extent．If UDP detects an error in the received packet，it will silently drop it． The transport layer also provides a connection mechanism for the processes．The (3) must be able to send streams of data to the transport layer．It is the responsibility of the transport layer at (4) station to make the connection with the receiver, chop the stream into transportable units，number them，and send them one by one．It is the responsibility of the transport layer at the receiving end to wait until all the different units belonging to the same process have arrived，check and pass those that are (5) free, and deliver them to the receiving process as a stream．

（4）处应填（）。

A．sending

B．routing

C．switching

D．receiving
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问答题 简答题

我国公民有哪些基本政治自由权？
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