What are the two primary drawbacks to the payback period method? a. Difficult to calculate; only works for long projects (e.g., 5 years or more) b. Ignores time value of money; ignores cash flows after payback is reached. c. Only works for long projects; ignores cash flows after payback is reached. d. Difficult to calculate; ignores cash flows after payback is reached e. Difficult to calculate; ignores time value of money