Where must an individual's conductor certificate be kept?

Answer: C — In the conductor's personal possession while on duty

An individual's conductor certificate must be kept in the conductor's personal possession while on duty to ensure that it is readily available for verification and compliance with regulations. Having the certificate on hand allows the conductor to provide proof of qualifications when required, demonstrating their capability to perform their duties safely and effectively. This practice underlines the importance of accountability and ensures that all regulatory and safety standards are upheld during operations. Additionally, keeping the certificate in personal possession fosters a sense of professionalism and responsibility within the role, as conductors must be prepared to present their credentials to management or inspectors at any moment. This requirement aligns with best practices in the industry, promoting a culture of safety and preparedness among train crew members.