GInI’sCInP Handbookdefines the Design Thinking process with five steps: Empathize, Define, Ideate, Prototype, and Test. The fourth step is "Prototype," where teams build tangible representations of ideas, but the question specifies the "activity associated with ‘Test’" in the "fourth major step." This likely reflects a numbering error—Test is fifth, not fourth. Assuming intent is the Test step, GInI describes it as "testing solution prototypes" to gather feedback, refine concepts, and validate assumptions. Option A, "Building solution prototypes," is the Prototype step’s activity (fourth). Option B, "Ideating / brainstorming," is third. Option C, "Testing hypotheses," is broader and earlier (Define). Option D matches GInI’s Test definition, aligning with the original answer, correcting for the step mislabeling, and emphasizing GInI’s iterative feedback loop—a critical mechanism for solution refinement.