It's "think".

[ He's blushing now, and he hopes his hair can hide some of it when he's leaning over his notebook. ]

Come on, we still need to pick a real topic before we can start eating or I can start tutoring you in how to speak actual English.

[ Even though he clearly had no idea? What was his sister's class learning right now? ]

Let's do a presentation about the Heian period.