What do we mean by "to heat again"?

The term "to heat again" directly corresponds to the action of warming something up that has already been heated. In this context, "rehat" is the most fitting choice because it clearly conveys the intended meaning of applying heat to something a second time. This action is commonly used in cooking or warming food that has cooled down, making it a straightforward and precise definition.

The other options refer to different actions: to "rewarm" implies heating something up again, but "reheat" is a more specific and commonly used term in various contexts. "Refuse" means to decline or reject something, and "reactivate" suggests bringing something back to life or making it operational again, which does not relate to the act of applying heat. Thus, "rehat" is the best choice because it succinctly encapsulates the meaning of heating something a second time.