before何时是连词何时是介词
问题描述：
before何时是连词何时是介词
答
before既可以做介词,又可以做连词,意思是"在^之前".后面接句子时,是连词,如：
I had taught in that school before I moved here.
before后面接单词或者短语时,是介词.如：
He came here before 12 o'clock.