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[音频]Man has been polluting the earth from the time he first made fire, washed his clothes in the river and threw his waste on the ground. When land was used up or water became (1)______ , man moved on to another place. At first it was all right because there was plenty of clean air, land and (2)_______ . And there were (3)_______ people. But the growing population and modern industry have changed the situation. Today, pollution has brought serious (4)______ to our health and life.
梁底部纵筋的原位标注错误的是（ ）
梁的原位标注包括 ( )
1、在两种商品，两个国家，两种要素的模型中，假定同种商品是同质的，两国的偏好也相同，则国际贸易发生的直接原因是（）。
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