Concept:A leftward shift of a supply curve represents a change in overall market supply, not just a movement along the curve.
Explanation:A supply curve shows the quantity a producer is willing to sell at each price.
When the entire supply curve shifts to the left, it means that at every price level, producers now offer a smaller quantity than before.
This is called a decrease in supply.
It is different from a reduction in quantity supplied, which would be shown by a movement along the same curve due to a fall in the commodity's own price.
A leftward shift is caused by external factors such as higher production costs, lower technology, fewer suppliers, or unfavourable government policies.
For example, if the cost of raw materials rises, producers supply less at each price, shifting the curve leftward.
Therefore, a leftward shift clearly indicates a decrease in supply.
Answer:B. A decrease in supply