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问题 单项选择题

渗透泵型控释制剂常用的半透膜材料

A．产生协同作用，增强药效
B．减少或延缓耐药性的发生
C．形成可溶性复合物，有利于吸收
D．改变尿液PH，有利于药物代谢
E．利用药物间的拮抗作用，克服某些药物的毒副作用

答案

参考答案：A

单项选择题

在进行数据查询时，用户编写的应用程序只对全局关系进行操作，而不必考虑数据的逻辑分片，这需要分布式数据库至少要提供______。

A．分配透明性

B．分布透明性

C．局部数据模型透明性

D．逻辑透明性
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单项选择题

A transport layer protocol usually has several responsibilties. 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）是（）

A.sending

B.routing

C.switching

D.receiving
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