他在黑暗的走廊里绊了一下，差点摔倒。

He ___stumbled in the dark hallway and almost fell.

她在演讲时突然卡壳，忘记接下来要说什么了。

She ___stumbled during her speech and forgot what to say next.

我在整理旧照片时意外发现了一张童年时的合影。

I ___stumbled across a childhood photo while organizing old pictures.