The correct answers that agree with the subject "everyone" are:
- is
- thinks
In standard English, "everyone" is considered singular, so it takes singular verbs. Therefore, "is" is correct, but the verb "think" should be in the singular form "thinks."
So the answers should actually be:
- is
- thinks (not just "think")
If you meant to ask about forms of verbs agreeing in the context of your selection, "is" is definitely correct, and if "thinks" were an option, it would be the right choice instead of "think."