我在清理阁楼时偶然发现了这些老照片。

I ___came ___across these old photos while cleaning the attic.

她昨天在网上偶然读到一篇有趣的文章。

She ___came ___across a fascinating article online yesterday.

我上周在城里偶然遇到了一位老朋友。

I ___came ___across an old friend in town last week.