The correct answer is D because, under NCMA CMBOK guidance, internal market research refers to the process of gathering and analyzing information within the organization to support acquisition planning and decision-making. This includes leveraging internal knowledge, historical data, lessons learned, and communication among organizational stakeholders such as program managers, contracting officers, and technical experts.

Option D---sharing information on contracting issues and trends with other managers---clearly reflects an internal activity, where insights and experiences are exchanged within the organization to improve procurement strategies and outcomes. This aligns with CMBOK's emphasis on collaboration and knowledge-sharing as key components of effective pre-award planning.

Option A is an example of external market research, as it involves reaching out to outside entities (customers of potential suppliers) to gather past performance data. Option B relates to cost analysis and budgeting rather than market research. Option C describes requirements definition, which is part of acquisition planning but not market research itself.

CMBOK highlights that both internal and external market research are essential, but internal research specifically focuses on organizational intelligence, enabling better-informed decisions, reducing risk, and improving alignment between requirements and acquisition strategies during the pre-award phase.