fall

1. She fell down on the ground and hurt her knee.

2. Be careful not to fall down the stairs.

3. The leaves are falling down from the trees.

这些例句展示了"fall down"在不同情境下的用法，包括描述人摔倒、提醒小心以及自然现象如树叶落下等。希望这些例子对你有所帮助。