The correct answer is A.
When the field excitation of a synchronous motor is increased, the magnetic field of the motor is strengthened. This causes the motor to draw more current from the supply, but the current is now in phase with the voltage. This means that the power factor of the motor has improved.
Option B is incorrect because the current drawn by the motor will increase when the field excitation is increased. However, the current will now be in phase with the voltage, so the power factor will improve.
Option C is incorrect because the power factor will improve when the field excitation is increased.
Option D is incorrect because the power factor will improve when the field excitation is increased.