What risk does a loose cover on a fill opening present?

A loose cover on a fill opening can significantly increase the likelihood of tampering. When a cover is not properly secured, it allows unauthorized individuals easier access to the fill opening, potentially leading to the introduction of contaminants or other hazardous materials into the fuel storage system. This could create safety hazards, including the risk of spills or improper fueling practices. Maintaining a secure cover is crucial not only for safety but also for maintaining the integrity of the fuel system.

While the other options address legitimate concerns related to fuel systems, none emphasize the security aspect as strongly as the opportunity for tampering. For example, reduced fuel supply efficiency acknowledges operational concerns, degraded fuel quality focuses on the potential for contamination, and increased fuel leak risk highlights safety hazards. However, the primary function of a secure cover is to prevent unauthorized access, which directly connects to the risk of tampering.