The correct answer is D. Synchronous motor.
A synchronous motor is an AC electric motor that rotates at a constant speed synchronous with the AC power supply frequency. The stator windings of a synchronous motor are supplied with AC power, which creates a rotating magnetic field. The rotor of a synchronous motor is made of a permanent magnet or a wound rotor with DC current applied. The rotor aligns itself with the stator magnetic field, and the motor rotates at the same speed as the stator field.
A DC motor is an electric motor that runs on direct current (DC). DC motors are typically used in applications where speed control is important, such as in power tools and electric vehicles. DC motors can be either brushed or brushless. Brushed DC motors have a commutator and brushes that switch the current to the rotor, while brushless DC motors have electronic switches that do the same thing.
A reluctance motor is an electric motor that uses the reluctance of the magnetic material in the rotor to create torque. Reluctance motors are typically used in applications where low cost and high efficiency are important, such as in fans and pumps. Reluctance motors can be either single-phase or three-phase.
A universal motor is an electric motor that can run on either AC or DC power. Universal motors are typically used in applications where size and weight are important, such as in vacuum cleaners and power tools. Universal motors are also known as series-wound motors because the stator and rotor windings are connected in series.
In conclusion, the only motor in which the stator and rotor fields rotate simultaneously is the synchronous motor.