Cost-benefit analysis is the most helpful tool to show risk reduction based on when developing risk treatment alternatives for a business case, because it compares the expected costs and benefits of each alternative and helps to select the most optimal and feasible one. Cost-benefit analysis also helps to justify the investment and resources required for the risk treatment plan and to demonstrate the value and return of the risk reduction. The other options are not the most helpful tools, although they may also be considered when developing risk treatment alternatives. Risk appetite, regulatory guidelines, and control efficiency are examples of factors or criteria that influence the selection of risk treatment alternatives, but they do not show the risk reduction based on the alternatives. References = CRISC: Certified in Risk & Information Systems Control Sample Questions