______ over and over again, but he still couldn’t understand.

A．Having explained

B．Having been explained

C．Explaining

D．It had been explained

某企业对销售员年销售额进行考核，则所考核的销售额是( )。

A．绩效考核的前提

B．绩效考核的内容

C．绩效考核的对象

D．绩效考核的条件