The correct answer is: D. Risk Free Rate
The certainty equivalent approach is a method of calculating the net present value (NPV) of a project by adjusting the cash flows to reflect the certainty of their occurrence. The adjusted cash flows are then discounted at the risk-free rate, which is the rate of return that an investor can expect to earn on a risk-free investment.
The other options are incorrect because they are not appropriate discount rates for the certainty equivalent approach. The accounting rate of return is a measure of profitability that does not take into account the time value of money. The internal rate of return is a measure of profitability that does not take into account the risk of the project. The hurdle rate is a minimum acceptable rate of return that is set by the company or the investor.
The certainty equivalent approach is a more conservative approach to project evaluation than the other methods. It takes into account the risk of the project by discounting the cash flows at the risk-free rate. This results in a lower NPV than the other methods, which may make the project appear less attractive. However, the certainty equivalent approach is a more accurate way to assess the value of a project.