21. Consider the market for aviation fuel. Assume downward-sloping demand curves and upward-sloping supply curves and positive equilibrium quantity. How many of the following events would cause an increase in the price paid by buyers under the new equilibrium? (1) Government encourages the use of trains by constructing more high-speed rail tracks. (2) The price of crude oil rises. (3) The use of robots in aircraft production reduces the marginal cost of aircraft production. (4) Government increases the tax on aviation fuel. A) 0 B) 1 C) 2 D) 3 E) 4 [ Answer21]