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.
2016春冀教版(三起)六下Lesson 12《Hellen Keller》ppt课件3
冀教版英语六下《Unit 4 Lesson27 I remember》PPT课件
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2016春冀教版(三起)六下Lesson 3《Let’s play》ppt课件1
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2016春冀教版(三起)六下Lesson 15《Jenny’s summer holiday》ppt课件5
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2016春冀教版(三起)六下Lesson 13《Summer is coming》ppt课件3
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2016春冀教版(三起)六下Lesson 11《Work hard》ppt课件3
2016春冀教版(三起)六下Lesson 15《Jenny’s summer holiday》ppt课件2
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冀教版英语六下《Unit 4 Lesson29 Surprise》PPT课件
2016春冀教版(三起)六下Lesson 11《Work hard》ppt课件2
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2016春冀教版(三起)六下Lesson 14《Tomorrow we will play》ppt课件2
冀教版英语六下《Unit 4 Lesson31 Are you ready for a quiz》PPT课件
2016春冀教版(三起)六下Lesson 13《Summer is coming》ppt课件4
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