题干

化学是以实验为基础的自然科学,通过实验可以得知物质的组成、结构、性质及其变化规律.下列通过实验得出的结论正确的是(   )

A:把燃着的木条插入某无色气体中,火焰熄灭,该气体一定是二氧化碳

B:白磷可以在氧气中燃烧,说明氧气具有可燃性

C:某物质经鉴定只含有一种元素,则该物质一定是单质

D:某反应属于置换反应,则一定生成单质和化合物

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答案(点此获取答案解析)

D

同类题2

阅读下面短文,掌握其大意,从短文后各题所给的四个选项A、B、C、D中,选出可以填入空白处的最佳选项。

      He met her at a party. She was outstanding; many guys were after her, but 1 paid any attention to him. After the party, he invited her for coffee. She was surprised. So as not to appear rude, she went 2.

      As they sat in a nice coffee shop, he was too nervous3say anything and she felt uncomfortable. 4, he asked the waiter, "Could you please give me some salt? I'd like to put it in my coffee."

     They stared at him. He turned red, but when the 5 came, he put it in his coffee and drank. Curious, she asked, "6 put salt in the coffee?" He explained, "When I was a little 7, I lived near the sea. I liked playing on the seaside ... I could feel its taste salty, like salty coffee. Now every time I drink it, I 8my childhood and my hometown. I miss it and my parents, 9are still there."

      She was deeply 10. That was the start to their love story.So they married and lived happily together.11 forty years, he passed away and left her a letter which said:My dearest, please forgive(原谅) my life-long 12. Remember the first time we dated? I was so nervous I asked for salt 13sugar. It was hard for me to ask for a change, so I just went ahead. Sweetheart, I don't exactly like salty 14. But as it mattered so much to you, I've learnt to enjoy it. If I could live a 15 time, I hope we can be together again, even if it means that I have to drink salty coffee for the rest of my life.