_________ is a device which converts electrical energy into mechanical energy.
Motor
A motor is an electrical machine or device that converts electrical energy into mechanical energy.
Speaker is a device in which electrical energy is converted into vibration then into sound energy.
An electric heater is an electrical device where electrical energy is converted into heat energy.
Television is a device in which electrical energy is converted into sound, light and unwanted heat energy.
So the correct option is (d).