Final answer:
Following the Surgeon General's announcement, the demand for chocolate decreases, leading to a reduced equilibrium price and a decrease in producer surplus.
Step-by-step explanation:
When the Surgeon General announces that eating chocolate increases tooth decay, this information negatively affects consumer preferences, leading to a decrease in the demand for chocolate. As demand declines, less chocolate will be sold at any given price, resulting in a lower equilibrium price of chocolate. Accordingly, the amount producers are willing to supply at each price also drops, illustrating a decrease in producer surplus since the price they receive and the quantity they sell both decline. Thus, the correct answer is D. decreases, and producer surplus decreases.