Cross Elasticity Indicates Substitutes

Steps:

• Review demand trends for sea journeys and alternative services (e.g., air or tunnel) over the period.
• Observe that sea journey demand declines while alternative demand rises.
• Infer the relationship: opposite demand movements suggest substitutes.
• Conclude positive cross elasticity from the proportional changes.

Why A is correct:

• Positive cross elasticity of demand (E_{xy} = %ΔQ_x / %ΔP_y > 0) measures substitutes, where data shows rising demand for one as the other falls, implying price or preference shifts favor the alternative.

Why the others are wrong:

• B: Data shows shifting market shares, not overall growth in total crossings.
• C: Decline occurs but without acceleration evidence in the trends.
• D: Complementary goods have negative cross elasticity; data shows opposite movements, not joint decline.

Final answer: A