To solve $x^{}m\cdot (\frac{1}{x})^{}n$, we multiply the (~\uline{~~~~~~~~~~~~~~~~~~~~}~)while keeping the (~\uline{~~~~~~~~~~~~~~~~~~~~}~) . 
选项为:A:base number, exponent  B:exponent, base number  C:I don\textquotesingle t know  D:I am gonna need a calculator  请回答其中一个选项.