The experimentation phase is the phase of design thinking when the ideas generated during ideation are tested and refined in the real world. This experimentation helps to identify the strengths and weaknesses of the proposed solution, leading to iterations and improvements before fully implementing the final design. Therefore, option C - implementation - is the best choice. Option A, inspiration, involves understanding the problem, empathizing with the users, and identifying opportunities for innovation. Option B, ideation, revolves around generating a variety of ideas and selecting the most promising ones. Option D, nonlinearization, is not a phase of design thinking.