Answer:
Their
Explanation:
Everyone is basically like using two or more peoples' names
Instead of everyone, we could replace it with Liam and Darcy to have 'Tell Liam and Darcy to bring ___ own lunch.
We cant use his in the blank because 'Tell Liam and Darcy to bring his own lunch sounds weird.
We cant use your because when you use peoples' names, you are using third person, and your is second person.
When you use their in the sentence, 'Tell everyone to bring their own lunch.', it sounds good and has a flow.
Hope this helps
