Beef is a normal good. You observe that both the equilibrium price and quantity of beef have fallen over time.Which of the following explanations would be most consistent with this observation?a. New medical evidence has been released that indicates a negative correlation between a person's beef consumption and life expectancy.b. The price of chicken has risen, and the price of steak sauce has fallen.c. The demand curve for beef must be positively sloped.d. Consumers have experienced an increase in income, and beef-production technology has improved.