They were waiting _____ the station _____ twenty minutes.

They were waiting _ the station _ twenty minutes.

Of - at

At - for

In - UpTo

None of these

"At the station": Indicates the location where they waited.

"For twenty minutes": Specifies the duration of waiting.

Use "at" for general locations (e.g., at the park, at home).

Use "for" to indicate duration (e.g., for hours, for days).