加法和减法叫做第一级运算，乘法和除法叫做第二级运算。
Addition and subtraction we call the first -progression operation, multiplication and division we call the second -progression operation.
加法和减法叫做第一级运算，乘法和除法叫做第二级运算。
Addition and subtraction we call the first -progression operation, multiplication and division we call the second -progression operation.
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