The correct answer is: D. All above can be used.
A drum type controller, a three point starter, and a four point starter are all types of controllers that can be used for D.C. motors of H.P. 12 or more that require frequent starting, stopping, reversing, and speed control.
A drum type controller is a type of controller that uses a drum with a series of contacts that are arranged in a specific pattern. The contacts are connected to the motor and to a power source. When the controller is turned on, the contacts close and allow power to flow to the motor. The pattern of the contacts determines the speed of the motor.
A three point starter is a type of controller that has three terminals: a common terminal, a start terminal, and a stop terminal. The common terminal is connected to the power source. The start terminal is connected to the motor. The stop terminal is connected to the controller. When the controller is turned on, power flows from the power source to the common terminal, to the start terminal, to the motor, and back to the power source. When the controller is turned off, power is cut off from the motor.
A four point starter is a type of controller that has four terminals: a common terminal, a start terminal, a stop terminal, and a field terminal. The common terminal is connected to the power source. The start terminal is connected to the motor. The stop terminal is connected to the controller. The field terminal is connected to the field winding of the motor. When the controller is turned on, power flows from the power source to the common terminal, to the start terminal, to the motor, to the field terminal, and back to the power source. When the controller is turned off, power is cut off from the motor and the field winding.
All three types of controllers can be used for D.C. motors of H.P. 12 or more that require frequent starting, stopping, reversing, and speed control. The type of controller that is used will depend on the specific requirements of the application.