(1) pay off = pay in full and be free obligation 还清（全部）债务。例如：[文章版权 禁止转载:考试与评价 http://www.trgroup.com.cn/te/ n(U8kuDLLlBU:(.FroG]

    After years of hard work, they paid off all their debts. 经过几年的辛苦劳动，他们还清了所有的债。[文章版权 禁止转载:考试与评价 http://www.trgroup.com.cn/te/ ~`Sy(2h
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    (2) pay back = return，意为“归还；偿还”。例如：[文章版权 禁止转载:考试与评价 http://www.trgroup.com.cn/te/ w0znT4X6p"g%g{QFroG]

    You must pay back all the money that I lent you. 你必须把我借给你的钱全部还给我。[文章版权 禁止转载:考试与评价 http://www.trgroup.com.cn/te/ 3YJM:k :o1 FnFroG]

    (3) pay for = spend some money on...，意为“付钱；支付；付出代价”。例如：[文章版权 禁止转载:考试与评价 http://www.trgroup.com.cn/te/ |=PIQ=4w kqN}yn=FroG]

    I have paid 100 dollars for it. 我已经为此付了100美元。[文章版权 禁止转载:考试与评价 http://www.trgroup.com.cn/te/ o]"dC) ,_gF:A?itOFroG]