1. 非谓语动词的否定式均为not+非谓语动词
现在分词的否定形式 not + 现在分词（完成的否定式not 放在having之前）
Not knowing how to dye the silk red, he went to her for help.
Not having heard from her son for a long time, the mother worried a great deal.
2. 一些独立结构：
① Generally speaking (speak), we have learnt a lot in this school.
② Judging (judge ) from his appearance, he is somebody.
③ To tell ( tell ) you the truth, your work is terrible.
