据《金融时报》报道，西电东送、西气东输、青藏铁路等一批事关西部大开发全局的重点工程相继开工，2001年，国家支持西部开发的国债资金预算内资金超过往年，新开工12个重点工程，总投资在3 000亿元。实施西部大开发，西部是最大的受益者。在这个机遇面前，西部人需要树立“国家政策引导，开发市场运作”这样的机遇观。西部大开发必须靠国家行为，但要以最小的投入换取最大的产出，就必须遵循市场经济规律。

请运用所学的经济知识分析说明：

（1）“政策引导”和“市场运作”分别体现了经济学的什么道理？

（2）在西部大开发中为什么既要有国家政策引导，又要有市场运作？

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．

（1）处应填（）。

A．hop

B．port

C．route

D．packet