Which of the following would most likely cause a vertical supply curve to shift to the left?

• A. A decrease in the availability of a key input
• B. An increase in consumer income
• C. A technological improvement in production
• D. A reduction in government-imposed production taxes

Answer: (A)

Verified step by step guidance

1. Understand that a vertical supply curve represents a perfectly inelastic supply, meaning quantity supplied does not change regardless of price.
2. Recall that a shift to the left in the supply curve indicates a decrease in supply at every price level.
3. Analyze each option to see how it affects supply: an increase in consumer income affects demand, not supply; a technological improvement typically increases supply, shifting the curve right; a reduction in production taxes lowers costs, increasing supply and shifting right.
4. Focus on the option 'a decrease in the availability of a key input' which raises production costs or limits production capacity, causing supply to decrease and the supply curve to shift left.
5. Conclude that a decrease in the availability of a key input is the factor that would most likely cause the vertical supply curve to shift to the left.