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.
空气在我们周围。我们看不见，闻不到，也尝不到。但我们能感觉到风在吹。我们可以看到风在水面上移动波浪，在天空中移动云朵和树枝。风在移动空气。
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.
没有空气，我们无法呼吸。不可能有活的植物或动物。因为声音在空气中传播，没有空气就会有寂静。空气的运动可以支撑一架又大又重的飞机。
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.
空气是气体和水蒸气的混合物。空气中最重要的气体是氮和氧。78%的空气是由氮和21%的氧气组成的。几乎所有的生物都利用空气中的氧气。没有氧气火就不能燃烧