Marshall-Lerner Condition Steps:

• Devaluation improves the current account balance if the sum of the price elasticities of demand for exports (ε_x) and imports (ε_m) exceeds 1.
• If ε_x + ε_m < 1, the volume responses are insufficient, causing the import bill to rise more than export receipts, worsening the balance.
• Compute sums: A (0.3 + 0.3 = 0.6), B (0.6 + 0.9 = 1.5), C (1.2 + 0.5 = 1.7), D (1.2 + 1.2 = 2.4).
• Identify the option where sum < 1 as the case for worsening.

Why A is correct:

• Sum of elasticities (0.6) < 1 violates Marshall-Lerner condition, so current account worsens post-devaluation.

Why the others are wrong:

• B: Sum (1.5) > 1, current account improves.
• C: Sum (1.7) > 1, current account improves.
• D: Sum (2.4) > 1, current account improves.

Final answer: A