Which of the following statements do you think reflect sound economic thinking? Explain your answer. 

a. “I paid $1,800 for this economics course. Therefore, I’m going to attend the lectures even if they are useless and boring.” 

b. “Because we own rather than rent, and the house is paid for, housing doesn’t cost us anything.” 

c. “I own 100 shares of stock that I can’t afford to sell until the price goes up enough for me to get back at least my original investment.” 

d. “Private education is costly to produce, whereas public schooling is free.”