. . . . . . . . the end of a course, students usually have a party. A. in B. on C. at D. None of the above

The correct answer is: C. at

The preposition “at” is used to indicate a specific time

The preposition “in” is used to indicate a period of time. In this case, the period of time is the course itself.

The preposition “on” is used to indicate a specific day or date. In this case, the day is the day of the party.

The preposition “none of the above” is used to indicate that none of the given options are correct.

I hope this helps! Let me know if you have any other questions.