Providing professional engineering or geoscience services to the public in Canada is a regulated activity. A foundational responsibility is to hold and maintain the appropriate licence/registration in good standing, comply with the regulator’s requirements (fees, competence obligations where applicable, standards of practice, code of ethics), and practise only as authorized. That makes C the most essential responsibility among the options. Innovation (A) can be valuable but is not required to fulfil professional duties. Promoting the regulator’s goals (B) is not an essential role duty; professionals must comply with regulatory requirements and support public protection, but they are not mandated promoters. Public outreach (D) may be beneficial but is not a core requirement for all practitioners. Therefore, maintaining a current licence in good standing (C) is the essential responsibility.