Which of the following statements regarding the heckscher-ohlin model and Ricardian trade theory is TRUE?
a. Both the Heckscher-Ohlin and Ricardian models are current, relevant, and applicable in explaining world trade patterns
b. The Ricardian model is an excellent simplified introduction to world trade patterns, but the Heckscher-Ohlin model is more relevant in regards to explaining empirical evidence
c. The Ricardian model is useless in explaining trade patterns, and the H-O theory, though applicable, is not sufficient for explaining real world trade patterns
d. The Ricardian model is extremely useful in analyzing trade patterns, but the H-O model is only useful in theoretical applications.