她在黑暗的走廊里绊了一下，差点摔倒。

She ___stumbled in the dark hallway and almost fell.

他在回答问题时结结巴巴，明显很紧张。

He ___stumbled over his words when answering the question, clearly nervous.

我在整理旧照片时偶然发现了这张珍贵的全家福。

While organizing old photos, I ___stumbled upon this precious family portrait.