The correct answer is C) blown fuse or tripped circuit breaker in the motor circuit. When a refrigeration compressor motor fails to start, the first thing that should be checked is the electrical supply to the motor, as a blown fuse or tripped circuit breaker in the motor circuit is the most common cause of this issue. Verifying the integrity of the electrical components ensures that the motor is receiving the necessary power to start and operate properly. The other answer choices, such as issues with the suction pressure regulator, high-pressure cutout, or expansion valve control bulb, are less likely to be the root cause of a failure to start. These components are more likely to affect the operation of the refrigeration system once the motor is running, rather than preventing the motor from starting in the first place.