状语从句怎么改非谓语动词

当状语从句的主语和主句的主语一致,并且含有be动词,或者状语从句中含有it is,我们可以把状语从句的主语和be动词（或it is）省略,这一块应属于省略的内容,但其实非谓语动词需要这样来理解.请看例子：
例1：When i was walking in the street,i saw him.
可以变为：1）When walking in the street,i saw him.(其实这也是连词+分词的结构）
也可以变为2）Walking in the street,i saw him.
(这时分词walking的逻辑主语就是句子的主语i,之间是主动关系I walk)
例2：When the park is seen from the top of the hill,the park looks beautiful.
可以变为：1）When seen from the top of the hill,the park looks beautiful.(连词+分词的结构）
2）Seen from the top of the hill,the park looks beautiful.
(这时分词Seen的逻辑主语就是句子的主语the park,之间是被动关系see the park)所以,当状语从句的主语和主语的主语保持一致（也就是说分词的逻辑主语就是句子的主语）,如果是主动关系,我们就用现在分词；如果是被动关系,就用过去分词.
例3：When i was passing by,a man was hit by a car.
但如果从句的主语和主句的主语不一致（也就是说分词的逻辑主语不再是句子的主语）,我们就要采用独立主格结构,这句话应改为：
I passing by,a man was hit a car.
或者：(when) passing by,i saw a man was hit by a car.
例4 If it is possible,please call me in time.可改写为If possible,please call me in time.(当然这句话不是分词,只是用来解释我上面所说省略it is 的情况)
自己敲了半天,