21. Which of the following statements is true? a. The contribution of a project to a firm's value is simply the NPV of the project. b. When the NPV profile of the project is not a downward sloping curve, applying the NPV rule (Le., if NPV is positive accept the project) may lead to a wrong investment decision. c. When a firm is evaluating a single project, NPV and IRR typically do not lead to the same conclusion regarding the profitability of the project. d. All of the above statements are true. e. Only a and c are true statements.