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问题 选择题

洁净的空气中性质比较活泼的化合物是（　　）

A．氮气

B．氧气

C．二氧化碳

D．某种稀有气体

答案

A、氮气是由氮元素组成的纯净物，属于单质．

B、氧气是由氧元素组成的纯净物，属于单质．

C、二氧化碳是由氧元素和碳元素组成的纯净物，属于化合物，二氧化碳的化学性质比较活泼．

D、每种稀有气体都是由一种元素组成的纯净物，属于单质．

故选C．

完形填空

Directions: Complete the following passage by using ONE word thatbest fits the context.

Deciding what present you should give someone is never easy.  Many things must be considered such as  1  the person is interested in and how old he is.   We must also consider the reaction   2  the person receiving the gift.  One of the worst gift choices I ever made was for my high school English teacher, Ms Chen. Ms Chen has taught me English since Junior 1, and to show my appreciation I  decided to get   3  a present.  I asked my classmates about her interests  4  I made my final decision.  

Then I went to the department store5 I worked part-time and bought her  6  expensive gift box of Sichuan beef.  I was certain she would like it  7  I had been told by my classmates that she loved hot food. I left the box with a card on her desk, and I was sure she would like them.8 was only after I heard she became sick that I learned she couldn’t eat MSG !
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填空题

家庭电路中电流过大的原因：一是 _________ ，一是 _________

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