They prepared a letter of apology _____ being late.

• A. For
• B. To
• C. Of
• D. About

Answer: (A)

The main idea here is using the right preposition with the expression apology for, which links the apology to its reason. When you apologize, you commonly say sorry for something—the reason you’re apologizing. So after a phrase like a letter of apology, you introduce the reason with for. In this sentence, being late is the reason, and the gerund phrase being late fits perfectly after for: they prepared a letter of apology for being late.

The other prepositions don’t fit the natural pattern. To would typically point to the person receiving the apology, not the reason, and about or of wouldn’t introduce the cause in this standard collocation.