Babies often fall down when they are learning to walk.
小儿学步时常会跌交。
There's nothing to be afraid of. The sky won't fall down.
没有什么好怕的.，天不会塌下来。
You are likely to fall down on your research project if you don't go to the experts for advice.
如果你不去向专家们请教，你的研究项目很可能夭折。
She didn't want to fall down like other leaves.
她不想像其他树叶一样落下。
She saw the leaves fall down.
她看到树叶飘落。