Air Around Us
Air is around us. We can not see it, smell it, or taste it. But we can feel the wind blow. We can see the wind move waves on the water, clouds in the sky, and tree branches. Wind is moving air. Without air we could not breathe. There could be no living plants or animals. Because sound travels through air, without air there would be silence. The movement of air can support a large, heavy plane. Air is a mixture of gases and water vapor. The most important gases in the air are nitrogen and oxygen. 78 percent of the air is made up of nitrogen, and about 21 percent of oxygen. Almost all living things use the oxygen in air. Fire cannot burn without oxygen. ?
2017届高考英语一轮复习梯级训练: Unit 1(人教版必修5)
2017届高考英语一轮复习梯级训练: Unit 2(人教版必修2)
2017届高考英语一轮复习梯级训练: Unit 4(人教版必修3)
2017届高考英语一轮复习梯级训练: Unit 4(人教版选修8)
2017届高考英语一轮复习梯级训练: Unit 1(人教版必修1)
2017届高三英语一轮复习同步课件:Unit 4 Period 3(人教版选修六)
2017届高考英语一轮专题复习阅读理解训练(21)含答案
2017届高考英语一轮复习梯级训练: Unit 4(人教版必修2)
2017届高考英语一轮复习梯级训练: Unit 2(人教版必修1)
2017届高考英语一轮专题复习阅读理解训练(13)含答案
2017届高三英语一轮复习同步课件:Unit 5 Period 1(人教版选修六)
2017届高考英语一轮复习阅读理解训练 (12)
2017届高考英语一轮专题复习阅读理解训练(6)含答案
2017届高考英语一轮复习阅读理解训练 (11)
2017届高考英语一轮专题复习阅读理解训练(20)含答案
2017届高考英语一轮复习梯级训练: Unit 1(人教版选修6)
2017届高考英语一轮复习阅读理解训练 (19)
2017届高考英语一轮专题复习阅读理解训练(8)含答案
2017届高考英语一轮专题复习阅读理解训练(22)含答案
2017届高考英语一轮复习阅读理解训练 (4)
2017届高考英语一轮复习阅读理解训练 (7)
2017届高考英语一轮复习梯级训练: Unit 4(人教版选修6)
2017届高考英语一轮专题复习阅读理解训练(15)含答案
2017届高三英语一轮复习同步课件:Unit 4(人教版选修六)
2017届高考英语一轮复习梯级训练: Unit 1(人教版选修7)
2017届高考英语一轮复习阅读理解训练 (17)
2017届高考英语一轮复习阅读理解训练 (5)
2017届高考英语一轮复习梯级训练: Unit 4(人教版必修4)
2017届高考英语一轮专题复习阅读理解训练(9)含答案
2017届高考英语一轮复习梯级训练: Unit 4(人教版必修1)
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