The correct answer is C) Number, position and angle of lashes. When loading and securing vehicles on a Ro-Ro (roll-on/roll-off) vessel, the primary concern is the proper securing of the vehicles to prevent them from shifting or moving during the voyage. The number, position, and angle of the lashings (also known as tie-downs or securement devices) used to secure the vehicles are critical factors to ensure the stability and safety of the cargo. Regulations and industry best practices dictate the specific requirements for the number, placement, and angle of the lashings based on factors such as vehicle weight, size, and the sea conditions expected during the voyage. The other options are not the primary concerns when loading and securing vehicles on a Ro-Ro. The number of axles (A) is not as crucial as the securing of the vehicles. Disconnecting the battery cables (B) is a fire safety measure, but not the primary focus for loading and securing the vehicles. Minor air pressure changes in the tires (D) are not a significant factor in the overall securing of the vehicles.