Hot chocolate is made from chocolate syrup and milk. Using a separate supply and demand graph for each question, please show the effects of the following events on the market for hot chocolate (please specify the change in demand, supply and the equilibrium):
a. A cold winter makes people more willing to buy hot chocolate.
b. a decrease in the price of chocolate syrup
c. a decrease in the price of tea (a substitute)
d. a decrease in the supply of milk