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问题 选择题

通常火灾是用水扑灭，原理是（　　）

A．水能冲淡可燃物周围的空气

B．水能降低可燃物的着火点

C．水遇火蒸发而吸热，有利于使燃烧物的温度迅速降到着火点以下

D．水容易获取，价格便宜

答案

根据灭火的原理回答：（1）清除可燃物或使可燃物与其他物品隔离（2）隔绝氧气或空气（3）使温度降到可燃物的着火点以下．因此

A、水能冲淡可燃物周围的空气，是错误的；

B、可燃物的着火点是一定的，水是不能降低可燃物的着火点的，故错误；

C、水遇火蒸发而吸热，有利于使燃烧物的温度迅速降到着火点以下，达到灭火的目的，故正确；

D、水容易获取，价格便宜，不是水灭火的原理，故错误．

故选C．

选择题
同时抛掷2枚质地均匀的正方体骰子，骰子的6个面上分别刻有1到6的点数，下列事件中是不可能发生事件的是

A.点数之和是12
B.点数之和小于3
C.点数之和大于4小于8
D.点数之和为13
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单项选择题

We once had a poster competition in our fifth grade art class.

"You could win prizes," our teacher told us as she wrote the poster information on the blackboard. She passed out sheets of construction paper while continuing. "The first prize is ten dollars. You just have to make sure that the words on the blackboard appear somewhere on your poster. "

We studied the board critically. Some of us looked with one eye and held up certain colors against the blackboard rocking the sheets to the right or left while we conjured up our designs. Others twisted their hair around their fingers or chewed their erasers while deep in thought. We had plans for that ten- dollar grand prize, each and every one of us. I’m going to spend mine on candies one hopeful would announce while another practiced looking serious wise and rich.

Everyone in the class made a poster. Some of us used parts of those fancy paper napkins, while others used nothing but colored construction paper. Some of us used big designs and some of us preferred to gather our art tidily down in one comer of our poster and let the space draw the viewer’s attention to it. Some of us would wander past the good students’ desks and then return to our own projects with a growing sense of hopelessness. It was yet another grown up trick of the sort they seemed especially fond of making all of us believe we had a fair chance and then always—always—rewarding the same old winners.

I believe I drew a sailboat, but I can’t say that with any certainty. I made it. I admired it. I determined it to be the very best of all of the posters I had seen and then I turned it in.

Minutes passed.

No one came along to give me the grand prize and then someone distracted me and I probably never would have thought about that poster again.

I was still sitting at my desk thinking, what poster When the teacher gave me an envelope with a ten-dollar bill in it and everyone in the class applauded for me.

The underlined phrase in paragraph 3 most probably means （）.

A．formed an idea for

B．made an outline for

C．made some space for

D．chose some colors for
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