Ali is considering the decision of whether or not to go and study a Master degree. He is currently working as an accountant in XYZ Company. He is thinking of getting a Master Degree. If he decided to study the Master Degree, he would expect to earn higher salary than his current one. On the other hand, the study of the Master Degree would force him to take unpaid leave from his current job. Furthermore, Ali recently purchased a new car. For Ali, the expected increase in salary after the Master Degree is referred to as: Select one: O a. Opportunity Revenue O b. Sunk revenue O c. Differential cost O d. Opportunity cost O e. Differential revenue