Here are the completed sentences based on the prompts given:

1. Mai enjoys writing short stories when she has free time.
-> Mai is **a short story writer**.

2. Jill doesn't run as fast as Tom.
-> Tom runs **faster than Jill**.

3. No one in the class is more intelligent than Peter.
-> Peter **is the most intelligent** in the class.

4. When did your father start working in this factory?
-> How long **has your father been working in this factory?**

5. She is the most beautiful girl I have ever known.
-> I've never **met anyone more beautiful than her**.