【观察】观察下列几组句子中动词-ing形式的用法，然后加以总结。
1. a. The children ran out of the room, laughing and talking.
b. Seeing nobody at home, Linda decided to leave them a note.
2. a. Having eaten too much for supper, my little brother couldn’t go to sleep.
b. Having worked with the foreigners for years, I knew them very well.
3. a. Not knowing her phone number, we couldn’t get in touch with her.
b. Not having received a reply, James decided to send another email.
