already 用于完成时态的肯定句.表示“已经”例如:I have already finished my homework.He has done it already.yet 多用于疑问句和否定句,表示“还”例如:Have you finished your homework?No,not yet.I have not yet finished my homework.Yes,I have already.ever 多用于疑问句,表示“曾经”.Have you ever been to Beijing?否定句用“never".Ihave never been to Beijing.