A. turnaround - This term typically refers to a change in direction or a reversal of a situation. It doesn't fit well in the context of a gathering or convention.

B. turnover - This term is often used in business contexts to refer to the rate at which employees leave a company and are replaced. It doesn't convey the idea of a gathering or attendance.

C. turn-out - This term is commonly used to describe the number of people who attend an event or gathering. In the context of a convention, "turn-out" is the most suitable term to convey the idea of the largest number of writers attending.

D. turn-on - This term usually refers to something that excites or interests someone. It doesn't convey the idea of a gathering or convention.

Therefore, "turn-out" is the most appropriate option as it accurately represents the number of writers present at the convention in Ilesa.