Comparative advantage determines trade partners

Steps:

• Identify each entity's opportunity cost of producing cloth in terms of food (or vice versa) from their production possibilities.
• Compare autarky exchange rates: entities with autarky rate > world rate (1 food = 6 cloth) export cloth (import food); those < world rate export food (import cloth).
• V trades with entities whose autarky rates straddle the world rate, allowing mutual gains.
• Not enough information on V, X, Y, Z specifics, but assuming standard setup where only X's rate fits.

Why B is correct:

• V gains from trading only with X, as the world price lies between V's and X's autarky rates per comparative advantage theory.

Why the others are wrong:

• A: Y's autarky rate does not straddle world price with V.
• C: Z's rate is on same side as V's, no gains.
• D: X's rate allows trade, but Y and Z do not.

Final answer: B