题目

下列运算正确的是（ ）A．B．C．D． 答案：【答案】B【解析】根据合并同类项法则、幂的乘方法则、同底数幂的乘法法则和积的乘方法则逐个判断即可．解：A、，故该选项错误；B、，故该选项正确；C、，故该选项错误；D、，故该选项错误；故选：B． I told Sally how to get here, but perhaps I ______for her.A．had to write it outB．must have written it outC．should have written it outD．ought to write it out