Walking along the street,I met Mary.
I met Mary when I was walking along the street.
时间状语从句
Turning to the left,you will see the shop.
If you turn to the left,you will see the shop.
条件状语从句
Seeing from the top of the tower,I saw a beautiful city.
When I saw from the top of the tower,I saw a beautiful city.
时间状语从句
He came to my birthday party without being asked.He came to my birthday although he wasn't asked.
让步状语从句