Concept:Cost elasticity of supply measures how responsive quantity supplied is to changes in production cost or price.
It reflects how efficiently producers can adjust their output.
Explanation:A producer with efficient and flexible production can respond quickly to changes in price or cost.
This makes supply elastic.
A producer that cannot increase output easily has inelastic supply.
Greater responsiveness of supply shows a higher level of productive efficiency.
Therefore, cost elasticity of supply serves as an indicator of productivity, not profit, national income, or a price index.
Answer:B. productivity