What supports the solicitation plan by determining the marketplace capability to perform the contract?

The correct choice focuses on market research, which plays a crucial role in supporting the solicitation plan by evaluating and understanding the capabilities of the marketplace to fulfill contract requirements. Market research involves gathering and analyzing data on potential suppliers, their capabilities, and overall market conditions. This research helps in identifying vendors that can meet the specific needs of the contract and ensures that the solicitation is directed toward qualified sources.

Through effective market research, organizations can gain insights into price ranges, service offerings, performance history, and the general landscape of suppliers. This information is essential for making informed decisions during the procurement process, establishing realistic expectations, and ensuring competitive pricing.

On the other hand, internal market research may lack the breadth and objectivity of external market research, single-source negotiation often limits competition by negotiating with one supplier, and sealed bidding primarily refers to the process of submitting bids rather than assessing marketplace capabilities. Thus, market research stands out as the method that directly supports understanding the capacity of the marketplace to meet the contract's demands.