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.
上一篇: 高一英语作文
牛津苏教英语六年级单元试题-上册Unit1-3
牛津苏教英语六年级单元试题-下册Unit1-2(2套)
冀教版六年级上Unit4《lesson26 Christmas cards》word同步测试题
牛津苏教英语六年级单元试题-上册Unit5
冀教版六年级下unit 2《Lesson 11 This is good for you》word同步测试题
牛津苏教英语六年级期中试题-上册
牛津苏教英语六年级期中试题-上册之二
冀教版六年级下unit 2《Lesson 12 Eat your vegetables》word同步测试题
牛津苏教英语六年级期末试题-下册毕业模拟考试
牛津苏教英语六年级单元试题-下册Unit3
牛津苏教英语六年级期末试题-下册
冀教版六年级上Unit4《lesson29 the christmas story》word同步测试题
冀教版六年级下unit 2《Lesson 9 Always eat breakfast》word同步测试题
牛津苏教英语六年级单元试题-下册Unit7
牛津苏教英语六年级单元试题-下册Unit2
牛津苏教英语六年级期末试题-下册专项练习题
牛津苏教英语六年级单元试题-上册Unit6
牛津苏教英语六年级单元试题-下册Unit5
牛津苏教英语六年级期末试题-上册
冀教版六年级上Unit3《Lesson23 Are you ready for a quiz》word同步测试题
牛津苏教英语六年级单元试题-下册Unit4
冀教版六年级下Unit4《Lesson 30 Good-bye》word同步测试包(含听力)
牛津苏教英语六年级期末试题-下册素质调研
冀教版六年级上Unit4《Lesson31 Are you ready for a quiz》word同步测试题
冀教版六年级上Unit3《Lesson20 Winter Fun》word同步测试题(一)
冀教版六年级下Unit3《Lesson 24 Again, please》word同步测试包(含听力)
牛津苏教英语六年级单元试题-上册Unit3
冀教版六年级下unit 2《Lesson10 Always brush your teeth》word同步测试题
牛津苏教英语六年级单元试题-上册Unit7
冀教版六年级下unit 1《Lesson 4 Where did you go》word同步测试题