Dixon Shuttleworth is considering three investment options. The first investment offers a 5% return for the first five years, a 10% return for the next five years and a 20% return thereafter. The third investment offers a constant 12% rate of return. Determine which of these investments is the best for Dixon if he plans to invest a lump sum today and keep his money invested for the following number of years:

A. 15 years

B. 20 years

C. 30 years