A. Heater will only become warm when switch is closed.
Explanation:
Switches are used to control the flow of electrons (basically electricity). If you look at the other trials, you see that when switch is open, the bulb or fan does not run cuz no electricity can get to them. But when switch is closed, electricity gets to them. Thus, they will experience similar thing with the heater I assume cuz they have not said anything about battery voltage or anything preventing heater from heating.
