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问题 选择题

分析推理是化学学习方法之一．下列实验推理中，正确的是（　　）

A．金属的冶炼方法与金属的活泼性有很大的关系，所以银和汞可以用热分解的方法冶炼

B．某雨水的pH小于5.6，说明雨水中一定溶解了SO2

C．糖尿病人应少吃含糖的食品，某八宝粥中注明未加糖，所以糖尿病人可以放心食用

D．将镁条和铝片用导线连接再插进稀NaOH溶液，镁条上产生气泡，说明镁比铝活泼

答案

A、因金属的冶炼方法与金属的活泼性有很大的关系，银和汞是不活泼金属，可以用热分解的方法冶炼，故A正确；

B、因某雨水的pH小于5.6，说明雨水中溶解了SO2或NO2，故B错误；

C、因八宝粥中的淀粉就是糖类，所以糖尿病人不能食用，故C错误；

D、根据原电池原理，镁条、铝片和稀NaOH溶液形成的原电池，铝片作负极，镁条作正极，不能说明镁比铝活泼，故D错误；

故选：A．

选择题

结合语境，下列句子中，得体的一项是[ ]

A．当同学向你请教问题时，你说：“有何见教？请问吧。”

B．当你骑车碰了别人的车时，你说：“对不起，没碰坏哪里吧？”

C．当老师到你家家访时，你说：“你是无事不登三宝殿啊！”

D．当朋友邀你看球赛时，你说：“快考试了，没空！”

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单项选择题

When the system upon which a transport entity is running fails and subsequently restarts, the (136) information of all active connections is lost. The affected connections become half-open, as the side that did not fail does not yet realize the problem.
The still active side of a half-open connections can close the connection using a (137) timer. This timer measures the time the transport machine will continue to await an (138) of a transmitted segment after the segment has been retransmitted the maximum number of times. When the timer (139) , the transport entity assumes that either the other transport entity or the intervening network has failed. As a result, the timer closes the connection, and signals an abnormal close to the TS user.
In the event that a transport entity fails and quickly restarts, half-open connections can be terminated more quickly by the use of the RST segment, the failed side returns an RST i to every segment i that it receives, when the RST i reaches the other side, it must be checked for validity based on the (140) number i, as the RST could be in response to an old segment, if the reset is valid, the transport entity performs an abnormal termination.

A．give-up

B．abandon

C．quit

D．connection
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