1.The house looked as if it was about to fall down.房子看起来好像就要倒塌似的。

2.If the blocks are placed off-centre, they will fall down.积木如果搭得中心错位就会倒塌。

3.Babies often fall down when they are learning to walk.小儿学步时常会跌交。

fall down后面接in某地，意思是掉落在某地