In our notes we learned about NPV profile graphs, which in those notes plot

a$.$The NPV on the vertical axis and the cost of capital on the horizontal axis

b$.$The return on investment on the vertical axis and the NPV on the horizontal axis

c$.$The NPV on the vertical axis and the payback period on the horizontal axis

d$.$The cost of capital on the vertical axis and NPV on the horizontal axis

e$.$The NPV on the vertical axis and the inflation rate on the horizontal axis