Before going to college, Yoram worked for a construction company as a salesman. After finishing college, Yoram went back to work at the same construction company, but was given a different role. What is the most likely reason he did not return to the salesman position? A His comparative advantage changed as he gained new skills B His college degree signaled an absolute advantage in tasks at the company C His marginal revenue product changed due to signalling D His old position was replaced by AI and automation.