副词从句的简化一般because，since，when，while省略，因为句子会暗示强烈的因果关系 但如果省略连接词会造成语义不清，则应该保留，或者用其他方法表示逻辑关系：

Although haveing nothing to do here,we can't leave early. Having nothing to do here, we still can't leave early.

如果有兼作介系词的连接词（before，after，since）存在，简化后只能接名词

Before being in school, he used to be a naughty child. Before being redecorated, the house was in bad shape Before redecoration, the house was in bad shape

当使用连接词或时态表示先后顺序时，可以不省略连接词或加上时态。

After writing the letter, he put it to mail Having written the letter, he put it to mail

避免悬荡修饰语，可以更改句子结构或使用独立主格，使用独立主格时应该注意将连接词省略。

Already sleeping soundly in bed,the child did not know it when her mother came to kiss her goodnight. The child already sleeping soundly in bed,her mother came to kiss her goodnight. The coffin (having been) interred,the minister said

PS：注意Ven有强烈的已完成意味，因此往往不需要完成时。 副词从句的连接词有表达某种逻辑关系的意义，简化时可以把连接词改为意思相近的介系词。

When she arrived at the party,she found all the people gone. Upon arriving at the party, she found all the people gone. Upon her arrival at the party, she found all the people gone. Upon completing the project,she was promoted Upon completion of the project,she was promoted Despite his opposition,the plan was carried out If there should be a fire, the sprinkler will be started In case of a fire, the sprinkler will be started Because the exam is only a week away, I have no time to waste. With the exam only a week away,I have no time to waste.