Demand Shift from Substitute Unavailability

Steps:

• Recognize that a demand curve shift to D' indicates a change in demand, not quantity demanded from price changes.
• Assume D' is rightward, showing increased demand for public transport.
• Identify non-price factors affecting demand, like substitutes or income.
• Evaluate options: only inability to drive removes a key substitute, boosting public transport demand.

Why B is correct:

• Per demand law, reduced availability of a substitute (car) increases demand for the good (public transport), shifting the curve right.

Why the others are wrong:

• A: Lower car costs make substitute cheaper, decreasing public transport demand (left shift).
• C: Lower public transport price causes movement along D, not a shift.
• D: Reduced services worsen supply, potentially decreasing demand (left shift).

Final answer: B