______ earlier,I would not have attended______ earlier,I would not have attended the Christmas party.What a big mistake I made!(1) Did I know(2) If I knew(3) By knowing(4) Had I known应该选几?要原因
问题描述：
______ earlier,I would not have attended
______ earlier,I would not have attended the Christmas party.What a big mistake I made!
(1) Did I know
(2) If I knew
(3) By knowing
(4) Had I known
应该选几?要原因
答