是before詞義“在...時間之前”,而since詞義是“自從.時間以來”,until是“一直到.時間”,顯然,后兩個詞的詞義是不合適的.那如果前面是過去式用什么？如果是完成時用什么呢？It was ten years before he came back.It had been ten years until/ before he came back.since在什么情況下用呀It has been ten years since he came back.It is ten years since he came back.since表示從過去一個時間點到現(xiàn)在，所以句中應(yīng)該是現(xiàn)在時態(tài)，現(xiàn)在完成時和一般現(xiàn)在時都屬于現(xiàn)在時態(tài)。