Grammar
1. 动词-ing的完成式是having done, 表示一个已完成的动作, 这个动作发生或完成在谓语动词表示的动作之前。如:
Having worked in this school for so many years, she knows it very well.
Having finished his homework, the boy went out to play.
3. 动词-ing完成式的否定式是not having done。如:
Not having studied his lessons very hard, he failed the exam again.
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