Concept:A thermostat automatically controls and stabilizes temperature.
Explanation:An incubator requires a constant, steady heat supply.
A thermometer only measures temperature; it cannot adjust it.
A hygrometer measures humidity, while a barometer measures air pressure.
A thermostat senses temperature changes and switches the heat source on or off.
This action keeps the incubator’s heat stable and within the desired range.
Hence, the correct device is the thermostat.
Answer:D. thermostat