题干

2011年12月2日,我国在西昌卫星发射中心用长征三号甲运载火箭,成功将第十颗北斗导航卫星送入太空预定轨道,卫星所用的燃料是液态偏二甲肼[C2H8N2],氧化剂是N2O4,发生的反应可写作:C2H8N2+2N2O4=3N2↑+2CO2↑+nH2O↑.下列说法正确的是(  )


A:该化学方程式中n=3  

B:该反应是分解反应

C:反应前后原子总数发生变化

D:N2O4是氧化物

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答案(点此获取答案解析)

D

同类题3

阅读下面短文,从短文后各题所给的A、B、C和D四个选项中,选出可以填入空白处的最佳选项。

    I volunteer some of my time in order to give back just a little of what I am so blessed to have. This month. I had an unbelievable opportunity to 1 my dream, and step out of my 2 surroundings. I volunteered to go to Guatemale (危地马拉) with an eyeglass.

    Our 3 went to a small town in Guatemala. San Augustin. We 4 our tables and packages of pre-made 5in the dirt courtyard of a clinic, get up the Snellen chart on a wall, and began 6 people. Young and old, they came from many of the 7 town. Most had never had an eye exam before.

    They waited for hours8 in the sun, never complaining. If we could help them out with a 9 pair of glasses they would feel deeply 10. Some only left with eye drops or sunglasses, and 11 these people were grateful.

    We saw over a hundred 12 a day and a good part of those we saw got glasses. We 13over and over from people who knew their eyes 14help that they had not gone to a doctor because it was too 15, or had not got the glasses they needed for the same reason. We saw children who were16 out of school because they could not see the17, and we met women who could not see to thread needles, drivers with 18 seeing road signs.

      We are not doctors, and there were several people we could not help. But for those we could, we watched with pleasure as their lives19. What a gift sight is and what a difference it 20to see clearly.