The correct answer is B) machinery spaces. Automatic mechanical ventilation shutdown is required for CO2 systems protecting machinery spaces because machinery spaces are the most common location for fire hazards on a vessel. CO2 systems are an effective fire suppression method, but they can displace oxygen and create an asphyxiation risk. Shutting down the ventilation system prevents fresh air from entering the space and diluting the CO2 concentration, ensuring the fire is effectively extinguished. The other options are incorrect because cargo compartments, living quarters, and galleys do not have the same high fire risk as machinery spaces, so automatic ventilation shutdown is not required for CO2 systems in those areas.