题目内容：

____（not know）his telephone number,
（接上）she had some difficulty getting in touch with Bill.
空格填not knowing,为什么?

优质解答

因为没有连接词.,原来前半句是原因状语从句,原句是 because she didn't know his……
去掉连接词,主语也省略,谓语变成非谓语knowing 当然助动词也没有了 那么否定词还原成not 就是not knowing了