Which of the following statements is CORRECT? Please provide explaination why the choice is right

a.

An NPV profile graph shows how a project's payback varies as the cost of capital changes.

b.

The NPV profile graph for a normal project will generally have a positive (upward) slope as the life of the project increases.

c.

An NPV profile graph is designed to give decision makers an idea about how a project's risk varies with its life.

d.

An NPV profile graph is designed to give decision makers an idea about how a project's contribution to the firm's value varies with the cost of capital.

e.

We cannot draw a project's NPV profile unless we know the appropriate WACC for use in evaluating the project's NPV.