We were expecting them in the evening but they arrived … dawn.

Analyze the question The sentence is: "We were expecting them in the evening but they arrived ........... dawn." We need the correct preposition to go before "dawn."

Explain the concept Prepositions of time follow set patterns:

• on is used with days and dates (on Monday, on 5th May)
• in is used with longer periods (in the morning, in June, in 2014)
• at is used with specific points in time (at noon, at midnight, at night, at dawn, at sunrise)

Dawn is the exact moment daylight first appears, so it counts as a point in time. It takes at.

Solution

1. "Dawn" is a specific point in time, not a day or a long period.
2. "On dawn" is wrong because "on" is for days and dates.
3. "In dawn" is not idiomatic. We do not use "in" with dawn.
4. "For dawn" does not make sense here, because "for" shows duration or purpose.
5. "They arrived at dawn" is correct, and it matches the contrast in the sentence: they were expected in the evening but came much later, at daybreak.

Answer: B. at

Tip Remember the pattern "at + a precise moment": at dawn, at dusk, at noon, at midnight, at sunset. Use "in" for the parts of the day (in the morning, in the afternoon, in the evening). Night is the exception, because we say "at night."