The Earth 地球The earth is big.It is a big ，round ball. There are rocks on the earth. There is soil on the earth. There is water on the earth. 地球很大，它是一个又大又圆的球体。地球上有岩石，地球上有土壤，地球上有水。Look at the people on the earth. Do they fall off?看看地球上的人，他们会掉下去吗？Jump. You come down to the earth. Jump up again.You come down again.You always come down to the earth. 跳一下，你会落到地球上。再跳起来，你还会落到地球上。你总会落到地球上。The earth pulls things down .The pull of the earth is gravity. 地球能把物体吸引下来，地球的这种吸引力称作地球引力。词汇积累:rock 岩石 soil 泥土gravity 地球引力fall off 跌落 pull…down把…拉下来
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