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问题 单项选择题

口腔保健咨询时，关于氟化物对人体有害的说法，杨大夫是这样回答家长的

A．过量有害，可以不用
B．适量防龋，有益健康
C．过量无妨，多多益善
D．只能局部用，不能全身用
E．只能全身用，不能局部用

答案

参考答案：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 (71) numbers to accomplish this．Another responsibility is to providecontrol mechanisms at the transport level．UDP does this task at a very minimal level．There is no flowcontrol mechanism and there is no (72) for received packet．UDP, however,does provide errorcontrol 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 (73) must be able to send streams of data to the transport layer．It is the responsibility of the transport layer at (74) station to make the connection with the receiver,chop the stream into transportable units，numberthem，and send them one by one．It is the responsibility of the transport layer at the receiving end to waituntil all the different units belonging to the same process have arrived，check and pass those that are (75) flee，and deliver them to the receiving process as a stream．

A．hop

B．port

C．route

D．packet
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单项选择题

接地引下线导通测试值在（）间的设备状况尚可，宜在以后例行测试中重点关注其变化，重要的设备宜在适当时候检查处理。

A.10mΩ-50mΩ

B.50mΩ-200mΩ

C.200mΩ-1mΩ

D.1Ωm-2mΩ
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