[单选题]Do you forget to turn off the lights and heaters when you go out of a room? In 2040 it will not ___76___. They will turn themselves off and ___77___ again when you return. You will choose the temperature ___78___ each room, the lighting and the humidity. A sensor will detect the ___79___ of a human (and, with luck, ignore the dog!) and turn the systems on, and when the humans ___80___ it will turn them off again.The sensors will work ___81___ the central home computer, and they will do ___82___ more than just turn the fires and lights on and off for you. They will detect faulty electrical appliances, plugs or switches, isolate them ___83___ they cannot harm anyone, and then warn you that they need repair. They will detect fire and ___84___ you are out of the house, the computer will call the fire brigade. It will also call the police should the sensors detect an intruder. This will not be too difficult ___85___ the locks on the outside doors will be electronic. You will open them using your personal card—the one you use for shopping—maybe using a number known only to you.77____ A on B off C by D at