The given correct answer is "Design". In the context of the stages mentioned (Design, Development, Analysis, Documentation), the stage that involves validation is typically the Design stage. During the Design stage, the plans and specifications for the project are created and reviewed to ensure that they meet the desired objectives and requirements. This includes validating the design against the project's goals, constraints, and feasibility. The Development stage involves the actual implementation of the design, Analysis involves studying and understanding the problem or requirements, and Documentation involves creating and maintaining project documentation.