(a) (10 points) List three important features of the Ricardian Model. Why is the Ricardian model an influential theoretical framework in international trade? (b) (10 points) Compare the Ricardian model and the specific-factors model we introduced in the lec- tures. List three differences between these two models, and explain how the differences lead to different model predictions. (c) (10 points) Compare the specific-factors model and the Heckscher-Ohlin model we introduced in the lectures. List three differences between these two models, and explain how the differences lead. to different model predictions.