The correct answer is false
It is false that lighting a fire on a cold night to get warm is an example of positive reinforcement.
When referring to positive reinforcement, we understand is giving a reinforcing stimulus to award an action or expected behavior. The idea is that the conduct or behavior can be repeated in the future. Then, if we apply another positive reinforcement, the behavior can be expected again and again. And in the case of the question, it is false that lighting a fire on a cold night to get warm is an example of positive reinforcement.