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
______ 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
问题解答：
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