Ⅰ. ago adv. “……以前”指從此刻起，若干時(shí)間以前，通常與過去連用。如：

　　① It happened two days ago.這件事發(fā)生在兩天以前。

　　② 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(shí)起若干時(shí)間以前。通常與完成時(shí)、過去時(shí)等連用。還可用作前置詞或連接詞表時(shí)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(shí)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.

　�、� I never met him before.