Which scenario would result in the highest customer NPV?

a) 75% retention rate, a 10% required rate of return and the same customer profit in years 1 to 4

b) 75% retention rate, a 15% required rate of return and the same customer profit in years 1 to 7

c) 50% retention rate, a 50% required rate of return and the same customer profit in years 1 to 4

d) 75% retention rate, a 10% required rate of return and the same customer profit in years 1 to 5