采用石膏抹灰时,石膏灰中不得掺用()。
A、牛皮胶
B、硼砂
C、氯盐
D、107胶
参考答案:C
After three years of hard work, they at last _____ all the money they had borrowed.
A.paid off
B.paid back
C.paid in
D.paid for
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