(A) at
(B) of
(C) by
(D) None of these
🧠 Explanation:
In this context, “at” is the appropriate preposition to indicate a specific point in time when the action occurred. The phrase “at the end of” refers to a particular moment marking the conclusion of an event, meeting, or lesson. Using “in” or “on” here would be grammatically incorrect because they indicate duration or specific dates rather than a single moment. This structure is common in both spoken and written English to clearly pinpoint when an action takes place relative to the ending of another activity.
