用一条长400厘米的细绳围成以下图形，其中面积最大的是（   ）

一辆载满20t电石的挂车，在浙江滨江区燃起熊熊大火并伴有大量黑烟。事故路面上洒落了五六百米燃着的石头。这辆货车在雨中整整燃烧了一天，消防官兵对大火也束手无措，场面让人震撼。大家对电石的化学性质产生了浓厚的兴趣，请你一起与他们完成下列探究活动．

【查阅资料】电石的主要成分是碳化钙（CaC₂），可以与水反应生成一种可燃性气体及白色固体。常见的可燃性气体中，乙炔（C₂H₂）燃烧时伴有大量黑烟。

【猜想与假设】

电石与水反应生成的可燃性气体是：氧气、氢气或乙炔（C₂H₂）；同学们做出以上猜想的依据是____，大家讨论后，一致认为该气体不可能是氧气，原因是____。电石与水反应生成的白色固体是：氧化钙、氢氧化钙或碳酸钙中的一种。同学们经过讨论认为白色固体不可能是氧化钙，因为氧化钙会与水反应。

【实验探究】

实验步骤	实验现象	实验结论
⑴取适量电石加水反应，收集生成的气体，验纯后点燃．	气体燃烧，产生黄色火焰并伴有浓烈黑烟．	电石与水反应产生的气体是____
⑵取适量反应后生成的固体于试管中，滴加过量稀盐酸．	固体溶解，____	电石与水反应产生的固体不是碳酸钙
⑶取适量反应后生成的固体于试管中加水，向上层清液中滴加____．	溶液变红	电石与水反应产生的固体是氢氧化钙

【反思交流】请根据以上实验结论写出电石与水的反应的化学方程式____；

载有电石货车可以在雨中整整燃烧一天而不熄灭，说明电石与水反应是____（填“吸热”或“放热”）反应。

在蹦床比赛中，运动员在空中作竖直上抛运动的时间为2秒，则运动员跳离蹦床最高的高度为（g取10m/s²）

阅读理解
    As I grow up, I gradually know that life plays a very important role in my education I really wanted to achieve. What I mean is that life can teach you things no one else can. Luckily for you, it's time to have lessons of life. Pay attention and you can know what I call the school of life.
    Use Your Head
    You have to be smart to survive (生存) in this world. Anytime you need to make a move, stop and think. Obviously there will be times when you need to take action first, but if you've been taking the time to plan, you'll always make the right choice. Fail to plan, plan to fail.
    Set Your Goals
    In my team, if you don't finish the job well, we will fire you. Your goals should be on building a basic of solid and complete work. Make certain a list of what you have to do and start with the biggest and most difficult task. The key here is goals.
    Respect Your Superiors (上级)
    Your boss is in his position for a reason, no matter what you think of him. If he's not the best one, be patient—he'll be out of there soon. In the meantime, you have to respect him as your superior. That means following orders and closing your mouth. If you don't respect your boss, how will you expect the people under you to do the same?
    Keep Your Cool
    You should never let your emotions (情绪) control you. You should learn to keep calm. Never lose your cool when dealing in business, or it will ruin the whole thing.
    The school of life can be hard, but if you're smart and play your cards right, you can come out with an A⁺. Just treat every situation as a learning experience. I hope you've studied.

已知全集，集合，，那么集合等于(   　  )