5．独立主格结构与分词短语都可以转换为状语从句。但是独立主格结构转换为状语从句后，它有自己的逻辑主语，与主句的主语不一致；而分词短语转换为状语从句后，从句的主语与主句的主语一致。
If time permits, we'd better have a holiday at weekends.
转换为：Time permitting, we'd better have a holiday at weekends. 如果时间允许,我们最好周末去度假。
When we see from the hilltop, we can find the city more beautiful.
转换为：Seeing from the hilltop, we can find the city more beautiful. 从山顶上看，我们发现这个城市更美了。
还必须注意，分词结构的逻辑主语并不总是和主句的主语一致，也可以是主句的其他成分。
Searching for the thief in the city, it had taken the policemen a long time. 在城市里搜查小偷，花费了警察很长一段时间。（Searching短语的逻辑主语是主句中的policemen）