The correct answer is A) normally open, momentary contact start push button switch. In a simple motor controller ladder diagram, "Input A" typically represents the start signal for the motor. A normally open, momentary contact start push button switch is the most common type of input used to initiate the motor operation. When the button is pressed, it provides a temporary signal to the control system to start the motor. The other options are incorrect because: B) a maintained contact switch would keep the motor running continuously without a stop signal, C) a normally closed, maintained contact switch would prevent the motor from starting, and D) a normally closed, momentary contact stop button would stop the motor, but would not be the appropriate input for starting the motor.