—They are two dollars.
气体 | 氢气 | 氮气 | 氦气 | 氧气 |
液化温度℃ | ﹣253 | ﹣195.8 | ﹣268 | -183 |
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亚洲 | 非洲 | 拉丁美洲 | 欧洲 | 大洋洲 | 北美 | |
人口数量(亿人) | 41.66 | 10.33 | 5.88 | 7.32 | 0.35 | 3.51 |
人口自然增长率(%) | 1.1 | 2.3 | 1.1 | 0.1 | 1.3 | 1.0 |
面积(万平方千米) | 4400 | 3000 | 2056 | 1000 | 900 | 2400 |
It's half past seven in the morning now. Everyone is busy. The phone is ringing and Mary picks up the telephone. It's from Bob, who is a friend of Mary's brother. Her brother is the only boy in the family, so everyone loves him so much. They would like to do anything for him. "Sorry, but you can't speak with my brother Jim right now. He is very busy. He is having breakfast. My grandma is passing the milk to him. My parents are putting his books and homework into his schoolbag. My little sister Tina is putting on his shoes for him. Oh! Sorry! I can't speak to you now; I have to open the door for him. If not, he may be late for school!" Mary puts down the phone and opens the door in a hurry.
( 1 )非负数集合:{ …};
( 2 )负数集合:{ …};
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