Sure, here are the answers to your questions:
1. We sailed down the river.
down is a preposition here, indicating the direction of the sailing.
2. The plane took off.
off is an adverb here, indicating the manner of the taking off.
3. The carriage moved on.
on is a preposition here, indicating the direction of the movement.
4. He hurried across the hall.
across is a preposition here, indicating the direction of the hurrying.
5. He hid behind the door.
behind is a preposition here, indicating the position of the hiding.
6. The ant crawled up the wall.
up is an adverb here, indicating the manner of the crawling.
7. We all went in.
in is a preposition here, indicating the direction of the going.
8. Come down.
down is an adverb here, indicating the manner of the coming.
9. The rider fell off the horse.
off is a preposition here, indicating the direction of the falling.
10. We went along the path.
along is a preposition here, indicating the direction of the going.
11. Sit near the window.
near is a preposition here, indicating the position of the sitting.
12. Come along, let us go.
along is an adverb here, indicating the manner of the coming.
I hope this helps! Let me know if you have any other questions.