若x、y为实数，且y=x-4+4-x2+5，求x+y的平方根．

阅读文章，完成文章后的问题。

                                                                  Travel by train

      Jack loves traveling by train. Whenever he feels like traveling, he'd first think about taking a trip on the

rail. That is because he never has to bother to book (订) tickets or collect them in advance (提前). Going to

the station and buying a ticket are what he has to do.

      Traveling by train is also very comfortable. Most of the trains are air-conditioned, warm in winter and

cool in summer. Jack usually chooses a non-smoking section, taking a seat by the window so he can enjoy

the outside views. If it is a night train, the experience can be exciting. He just sleeps the whole night and the

next day, he will be in a new city. By the way, he never has to worry about his meals. The train provides

food around the clock. 

      Traveling by train has another advantage to offer: you may run into some old friends or you can listen

to people talking about something of your interest. Last week when he was on a train, for instance, he ran

into a primary school classmate. They didn't expect that they could bump into each other that way. Their

talk brought back many things: the games they played, the jokes they made on their peers and the funny

things they had done.

1. 请用简短的话概括文中提到的乘火车的三个优点。

     ________________________________________

     ________________________________________

2. How would you like to go to school? Why?

    ________________________________________

在抗体形成时

A．只有T细胞有免疫记忆

B．T细胞通过其细胞表面的个体型作为抗原受体

C．巨噬细胞在异常情况下，才做为辅助细胞

D．B细胞比T细胞增殖更多

E．NK细胞活跃

同一行政复议案件申请人超过5人的，推选1至（）名代表参加行政复议。

A.3

B.5

C.6

D.10

D煤矿采用井工开采方式，设计生产能力450万t/年，服务年限35年，基建施工年限5年，2009年1月1日开始建设。该煤矿基建工程分别由两家施工企业承担，井下有5个基建工作面。矿井开采的煤层上部岩层中有2个含水层，开采煤层周边有采空区和废弃井巷，并已探明采空区充水。
2010年4月25日13时，当班工人在井下第3基建工作面作业时，发现巷道局部有“冒汗”、渗水等透水现象，班长甲立即向调度室报告，但当班调度员接报后未采取任何处置措施。15时10分，第3基建工作面发生重大透水事故。事发时，井下有作业人员185人，紧急升井101人。经3天奋力救援，59人获救。事故导致21人死亡，4人失踪。
事故发生后，D煤矿深感事故应急救援工作的重要性。D煤矿针对可能发生的事故，编制了安全生产专项应急预案，内容包括：应急处置基本原则、应急组织机构及职责、预防与预警、应急处置、应急物资与装备保障。应急组织机构和人员的联系方式、逃生路线、标识和图样以及相关文件附在预案之后。专项应急预案经企业内部评审后印发，并报当地人民政府备案。之后，D煤矿组织开展了透水事故专项应急救援演练。

根据以上场景。回答下列问题：

简要说明一次完整的应急演练活动包括哪些内容。

喷油器的试验与调整内容有：喷油器（）的检查、喷油压力的试验与调整、喷雾质量的检查、喷油角度的检查。

A.协调性

B.密封性

C.喷雾性

D.有效性