Answer:
The answer to this question: Which would turn on if the temperature in the house decreased, would be: the furnace and the heat pump.
Step-by-step explanation:
The reason is that both work in order to restore normal, or slightly higher, heat temperatures to a home and are used to combat the cold from winter, and other, cold seasons.
While a thermostat is a device used to sense the changes in temperatures inside a home, and it works to re-establish the balance pre-set by the homeowners by either activating the air conditioner, it is the furnace, aided by the heat pump, that help bring the temperature back up by using energy, and in the case of the pump, by taking the heat from a cold environment and transfering it to where it needs to be warmer.