What must accompany the supplemental application form if it is developed?

The correct choice highlights the necessity for OMB (Office of Management and Budget) approval and Privacy Act information when a supplemental application form is developed. This is essential because any new form intended to collect information from applicants must comply with government regulations regarding data collection and privacy.

OMB approval ensures that the proposed information collection is justified, necessary, and that it does not create an unnecessary burden on applicants. This approval process typically involves a review of the form's purpose, the types of data being collected, and how that data will be used. Additionally, including Privacy Act information is crucial to inform applicants about how their personal data will be handled, safeguarding their privacy rights. It ensures transparency and compliance with legal requirements pertaining to the collection, use, and storage of personal information.

In the context of the other choices, while agency approval and OPM's consent can be important in certain processes, they do not specifically address the regulatory requirements that involve data collection forms. Similarly, a list of qualified candidates does not pertain to the development of a supplemental application form itself and therefore would not be relevant to this question.