Concept:A leftward shift of the supply curve shows a fall in the overall supply at every price level.Explanation:The supply curve shows how much producers are willing to sell at different prices.A change in price causes a movement along the same supply curve.However, a shift of the entire curve is caused by factors other than price, such as production cost or technology.When the supply curve moves to the left, producers offer less output at each price.So this indicates a decrease in supply, not just a reduction in quantity supplied.Answer:B. A decrease in supply.