Question

a thermostat registers an increase or a decrease in temperature. which would turn on if the temperature in the house decreased?
the furnace and the heat pump
the furnace and the air conditioner
the heat pump and the air conditioner
the heat engine and the heat pump

Explanation:

When the temperature in the house decreases, we need devices that can generate or supply heat. A furnace burns fuel (like gas or oil) to produce heat. A heat pump can also provide heat (in heating mode) by moving heat from the outside (even cold outside air has some heat energy) to the inside of the house. An air - conditioner is used for cooling (removing heat from the inside of the house and expelling it outside), so it would not be turned on when the temperature decreases. A heat engine is a device that converts heat into work (like in a car engine), not typically used for heating a house in the context of a thermostat - controlled home heating system.

Answer:

the furnace and the heat pump