18. The discount rate that makes the net present value of an investment exactly equal to zero is the: A) Internal rate of return. B) Payback period. C) Average accounting return. D) Profitability index, E) Discounted payback period. 19. The internal rate of return (IRR) rule can be best stated as: A) An investment is acceptable if its IRR is exactly equal to its net present value (NPV). B) An investment is acceptable if its IRR is exactly equal to zero. C) An investment is acceptable if its IRR is less than the required return, else it should be rejected. D) An investmentis acceptable if its IRR is higher than the required return by 2 percentage points, else it should be rejected. E) None of the above