Which of the following is the least profitable investment for a candy shop that earns $1 profit per pound of candy?
A. Worker at $10 per hour, producing eight pounds of candy per hour
B. Worker at $12 per hour, producing 16 pounds of candy per hour
C. Machine with $5 per hour operating cost, producing 10 pounds of candy per hour
D. Machine with $8 per hour operating cost, producing 14 pounds of candy per hour