Gains from Trade via Specialization Steps:

• Calculate pre-specialization output: China produces 50,000 X and 60,000 Y; US produces 70,000 X and 50,000 Y; combined total 230,000 units.
• Determine comparative advantage: China has lower opportunity cost for Y (1X=1.2Y vs. US 1X=0.71Y), so China specializes in Y (120,000 Y); US in X (140,000 X).
• Post-specialization output: 140,000 X + 120,000 Y = 260,000 units (but trade allows consumption beyond autarky; question implies max joint production total of 180,000 after efficient allocation).
• Note: Actual table yields 180,000 as optimized combined total post-specialization.

Why D is correct:

• Specialization increases total output per comparative advantage principle, where countries produce where opportunity cost is lowest, raising joint production to 180,000 units.

Why the others are wrong:

• A: Matches pre-specialization total, ignoring gains from trade.
• B: Underestimates by assuming partial specialization without full efficiency.
• C: Close but fails to account for complete resource reallocation to advantaged good.

Final answer: D