At a discount rate of 12%, which of the following would be preferred by an investor? a. A lump sum of $1,000 to be received at the end of six years. b. $120 at the end of every year for the next six years. c. $100 at the end of years 1-4 and $135 at the end of years 5 and 6. d. A perpetuity of $60 per year