Final answer:
The question relates to changes in market conditions, but the provided answer choices are not sufficient to determine the correct response regarding a decrease in the number of firms. The example of decreased demand due to an economic downturn is represented by a leftward shift in the demand curve, indicating a lower quantity demanded at every price level.
Step-by-step explanation:
A decrease in the number of firms in the market would be represented by a shift in the supply curve. However, the choices A, B, C and D seem to refer to movements along a curve or changes in price levels, which are typically associated with the demand curve, not the supply curve. The information provided in the question prompts hints at economic concepts but does not directly answer the student's question without additional context. Nevertheless, the decrease in demand due to lower incomes is shown by a leftward shift of the demand curve from Do to D₂.
Therefore, without a graph or more context it is unclear which letter corresponds to the correct answer, as we are talking about a shift, not a movement along the curve. A decrease in the number of firms typically leads to a leftward shift in the supply curve, indicating a decrease in supply. Now, regarding demand, a slow economy resulting in the loss of jobs and reduced working hours would decrease consumers' income, leading to a decrease in demand for goods like cars at every price level. The graphical representation of this concept shows the original demand curve Do shifting left to D₂. This reflects that, at any given price, the quantity demanded is lower than before.