When is the risk-adjusted discount rate approach considered preferable to the weighted cost of capital approach in determining the net present value of a project?

a. It is preferable when the projects under consideration differ significantly in the number of cash flows generated by the projects.

b. It is preferable when the projects under consideration differ significantly in their total return.

c. It is preferable when the projects under consideration differ significantly in their cash inflows.

d. It is preferable when the projects under consideration differ significantly in their risk characteristics.