举重运动员在举杠铃前常用“镁粉”搓手,这种镁粉的主要成分是Mgco3它属于
A.混合物
B.单质
C.盐
D.碱
答案:C
碳酸镁是由镁离子和碳酸根离子组成的化合物,属于盐.
故选C.
用所给单词的适当形式填空。
1. Our teacher told us _______ (stop) talking in class.
2. I didn't finish _______ (write) my test because I ran out of time.
3. Are you _______ (study) for an English test now?
4. Have you f1nished_______ (write) your homework?
5. His teacher wants him _______ (remember) the school rules.
6. Every year_______ (thousand) of foreigners come to visit Mount Tai.
7. I_______ (meet) my old friend when I was doing my shopping this afternoon.
8. Everyone will_______ ( have) a robot in their homes in 100 years.
9. There are a lot of old_______ (build) in Beijing. They are very beautiful.
10. I have lived in this apartment since I_______ (come) to America.
下列图象中能正确反映题中所描述的变化事实的是[ ]
A、接近饱和的氯化钠溶液中加入氯化钠固体
B、不饱和硝酸钾溶液升温
C、一定量水中加入浓硫酸
D、加热蒸发稀盐酸