Choice "D" is correct. Internal rate of return is defined as the discount rate at which the net present value of the project equals zero.Choice "a" is incorrect.  The number of years it takes to recover an investment is the payback period. Internal rate of return is defined as the discount rate at which the net present value of the project equals zero. Choice "c" is incorrect. Internal rate of return is defined as the discount rate at which the net present value of the project equals zero, not one.Choice "b" is incorrect. The weighted average cost of capital for financing a project is the financing cost weighted by the relative proportion of each source of funds for financing the total project.  Internal rate of return is defined as the discount rate at which the net present value of the project equals zero.