下列说法中，正确的是（ ）
A．任何纯净物都是由一种元素组成的
B．纯净物都是由同种分子构成的
C．一种单质只能由一种元素组成
D．所有的混合物是由不同种元素组成的
A、纯净物只含有一种物质，不一定含有一种元素，故A错误；
B、纯净物有些是由分子构成，而有些是由原子或离子构成，故B错误；
C、单质是由一种元素组成的纯净物，故C正确；
D、混合物是由两种或两种以上物质组成的，有可能由同种元素组成，如：氧气和臭氧组成的混合物，故D错误；
故选C．
| 选择方框中所给单词的适当形式填空，使短文通顺、连贯（每词只能用一次）。 | |
country. On my way home, my car stopped. I was out of gasoline (汽油) on a road away from a town. I decided to walk 1_____ the road until I found someone who could sell me some gasoline. I had walked almost a mile before I finally found a big house near the road. I was 2_____ to see it because it was getting dark. I 3_____ on the door and a"small" old lady with long white hair answered. She said, "I've been waiting for you for a long time. Come in, please. I got 4_____ ready for you." "But I've come here only for some gasoline." I answered.I didn't know what she was talking 5_____. I didn't understand her. "Oh, Tony! Gasoline? You used to love tea." I quickly explained that my car was out of gasoline, but she didn't seem to hear me. She just kept 6_____ me Tony and talking about how long it had been since she saw me. She was talking so 7_____ that I was anxious (急着) to leave. As soon as she went to get the tea, I went out of the house as 8_____ as possible. I was so happy when I saw another house by the road. I was able to get some gasoline. When I told the man about the old lady, he said,"Oh, that's Helen. She lives all by 9_____ in that big house She's strange, but she wouldn't hurt 10_____. She is still waiting for the man she was going to marry twenty-five years ago. The man was named Tony. The day before their wedding (婚礼), he went away and never came back.'' I understood! |