Final answer:
The correct option: leftward shift of the demand curve
A decrease in the quantity demanded of chocolate milk is represented by a leftward shift of the demand curve. This indicates a reduced quantity demanded at each price point and can affect the equilibrium quantity and price in a market, similar to a change in tastes affecting demand for other products.
Step-by-step explanation:
A decrease in the quantity demanded of chocolate milk is represented by a leftward shift of the demand curve. When the entire demand curve shifts to the left, it indicates that at the same price levels, the quantity demanded of chocolate milk has decreased. This can be due to factors such as a change in consumer tastes, an increase in the price of chocolate milk, or the availability of substitutes.
For instance, a change in tastes away from Postal Services would result in a similar outcome as a comparison: a leftward shift in the demand curve, along with a decrease in the equilibrium quantity and a decrease in the equilibrium price. This explains the broader economic principle that when demand decreases, it impacts both the price and quantity in the market.