2. Short answer (a) Which five countries does the United States trade with the most? Which inter- national trade concept better explains why these five countries are the United States' largest trade partners, the gravity model of trade or the Ricardian model of comparative advantage? Explain (b) Which international trade concept better explains why Canada produces and exports so much paper, the Hecksher-Ohlin model, the gravity model or idea of increasing returns to scale? Explain