�、�. ago adv. “……以前”指從此刻起，若干時間以前，通常與過去連用。如：

　�、� It happened two days ago.這件事發(fā)生在兩天以前。

　�、� I met him a few minutes ago.我在幾分鐘以前碰到他。

　�、�. before adv, prep & conj “……以前”指從那時起若干時間以前。通常與完成時、過去時等連用。還可用作前置詞或連接詞表時間，而ago則不能這樣用。

　　① He said that he had seen her two days before.他說他兩天前見到過她。(表從她說話那時起兩天前)

　�、� I had been fine the day before.(那天)前一天的天氣很好。

　�、� I’ve seen that film before.

　　④ I never met him before.