keep sth. in mind 这是本短语的标准用法;当sth.指代内容过长,或者是that从句时,就后置,典型的就是keep in mind that...(意即此时是没有it的)举个例子应该就清楚了:Keep in mind that you should turn off the light when you leave. 记住走时你要把灯关了。Turn off the light when you leave. Keep it in mind. 走时关灯。记住这点。(这里的it就指代前面整句)