玛丽在松动的石头上绊了一下。

Mary ___stumbled on the loose rocks.

我的阁楼太暗了，我绊了一下摔倒了。

My attic was so dark that I ___stumbled and fell.

他在马路牙子上绊了一下，但迅速恢复了平衡。

He ___stumbled over the curb but quickly regained his balance.