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问题 选择题

有人将瓜田里幼小的圆形西瓜套在方型筐内，收获了方型西瓜，

这种现象属于（  ）

A．遗传

B．变异

C．变态

D．分化

答案

答案：B

生物体的亲代与子代之间，以及子代的各个体之间在性状上存在着差异的现象叫做变异。

填空题

如果一个正方形的边长a厘米，那么4a表示（    ），a2表示（    ）。
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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．call

B．state

C．cost

D．error
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