Do you believe a firm must have a firm grasp of the concepts of differential cost, opportunity cost and sunk cost to be effective in making business decisions? Please be sure that your first post talks about these three different types of costs. Consider giving examples - especially if you have examples within your own employment experience. Or - you can look for some online resources that offer you some other facets of this topic to discuss so that it isn't just a rehash of the textbook. Don't forget to cite any resources that you use - even the textbook.