The sentence that correctly uses a gerund is:
"I was writing stories about true events in my spare time."
Explanation:
1. A gerund is a verb form that functions as a noun and ends in "-ing." In this sentence, "writing" is the gerund form of the verb "write."
2. The sentence uses the gerund "writing" as the subject of the sentence to describe the action that was being done in the past ("I was writing stories about true events").
3. By using the gerund form, the sentence correctly turns the verb "write" into a noun to convey the action of writing stories about true events.
This sentence fits the criteria for using a gerund correctly because it effectively turns the verb into a noun and maintains proper sentence structure.