ago 不能单独使用,而before可单独使用,且常与现在完成时或过去时连用。“一段时间+ago”表示从说话时刻算起的若干时间以前,常用于一般过去时;“一段时间+before”表示从过去某时起若干时间以前,与过去完成时连用。如:[文章版权 禁止转载:考试与评价 o#yd5�xB( LF:,'FroG]
My grandfather died five years ago, and my grandmother had already died three years before(=died eight years ago). 我的祖父五年前去世了;我的祖母比他早三年就去世了(=八年前就去世了)。[文章版权 禁止转载:考试与评价 WTW~hb?St~3PFroG]
I have never seen him before. 我以前从未见过他。[文章版权 禁止转载:考试与评价 ?_,1zuz#60X[)IjFroG]