Which of the following depicts a decrease in demand?

The correct choice represents a decrease in demand as a shift to the left of the demand curve. This leftward shift indicates that, at each price level, consumers are willing to purchase fewer goods than before. Factors that might lead to this happen may include a decrease in consumer income, a drop in preferences for the good, an increase in the price of substitute goods, or a decrease in the price of complementary goods, among others.

When demand decreases, it shows that the market is responding to changes in consumer behavior or conditions that negatively affect their willingness or ability to buy the good at existing prices. The new position of the demand curve reveals that for the same prices, the quantity demanded has fallen, which is visually represented by the demand curve moving to the left.

In contrast, a rightward shift indicates an increase in demand, while an upward slope or a flat demand curve do not illustrate changes in demand but rather refer to the characteristics of supply and demand interactions or specific market conditions.