Verified Answer :

The correct answer to this question would be using a pronoun such as His (the most correct form) or Him (a form used often but less correct).

✡ Answer: His ✡


- - Why?

This is because you need to fill in the blank with a word that makes this sentence understandable and complete.

In this case, I used a pronoun.

I'm not sure about "his" acting in the play next week.

✡Hope this helps!✡