Rolling down your sleeves when working around aircraft is important primarily for safety reasons, specifically to protect yourself from flying debris and flash fires. In the aviation environment, various hazards can be present, including loose objects that might be propelled by rotor wash, engine blasts, or other forces. Additionally, the risk of fire is a serious consideration around aircraft, especially with their fuel systems and electrical components. Having exposed skin can increase the risk of injury from these potential hazards.
The other choices, while they may have their merits, do not highlight the critical safety aspect. Proper ventilation is not a priority in this context, and maintaining a professional appearance, although valuable, does not address the immediate dangers present around active aircraft. Compliance with uniform regulations is also important, but it is secondary to ensuring the safety of personnel working in potentially hazardous conditions. Thus, the focus on protection against physical dangers makes the reason for rolling down sleeves not only relevant but essential.