To qualify for a physical security project, prospects are typically required to submit a bidder's questionnaire because it provides structured and standardized information about the company's capabilities, experience, resources, and compliance with project requirements. In procurement and Human Resource management practices, this document helps organizations evaluate whether a bidder is technically and operationally capable of performing the work. It ensures fairness, consistency, and transparency in the selection process by allowing all bidders to be assessed against the same criteria. While customer references and executive biographies provide useful background information, they are not as comprehensive or standardized. An intent- to-bid letter only indicates interest, not qualification. Therefore, the bidder's questionnaire is the most appropriate tool for determining eligibility and suitability for a security project, making option C the correct answer.