1.现在分词的完成式(having+过去分词)表示的动作发生在谓语动词所表示的动作之前或两个动作在时间上有一定的间隔。
例如:
Having written the letter，John went to the post office.
(=After he had written the letter，John went to the post office.
约翰写完信后，就去邮局了。
Having lived in Beijing for years，Lao Wang knows the city quite well.
(=As he has lived in Beijing for years，Lao Wang knows the city quite well.)
老王在北京住了多年，所以对这个城市很熟悉。
Having drunk two glasses of water, Xiao Ma felt a little better.
(=After he had drunk two glasses of water Xiao Ma felt a little better.)
小马喝了两杯水，感觉好一些了
一般式和完成式现在分词都可以表示先后接连发生的动作。在可能引起误解的场合应该用完成式现在分词表示先发生的动作。
例如:
Opening the drawer，he took out his wallet.
(=He opened the drawer and took out his wallet.)
他打开抽屉，拿出钱包。
Coming into the room，he put down his bag.
(=he came into the room and put down his bag.)
他走进房间，放下提包。
Having brushed his teeth，Mr. Brown came downstairs for breakfast.
布朗先生刷过牙，就下楼来吃早饭。
(此句如写成:Brushing his teeth, Mr. Brown came downstairs for breakfast.可能指“边刷牙，边下楼’。)
2.现在分词的被动语态(being +过去分词)通常表示“正在被…”的意思。如强调现在分词表示的动作发生在谓语动词所表示的动作之前时，可用现在分词被动语态的完成式(having + been +过去分词)。
例如:
The bridge being built will be completed next month.正在修建的那座桥将于下月完成。
Having been kept out of the room about half an hour for his returning late，Tom was let in.汤姆回来晚了，所以被关在门外半小时左右才让他进去。
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