Opportunity cost is the loss of potential advantages or gain caused due to you choosing one option from a number of alternate options. The answer to the question is D. You will earn less or no money for the period you are in college. For every choice you make, there is potential benefit as well as harms by choosing that option. As far as opportunity cost regarding choosing a college is concerned, different factors need to be considered. For example:
a. Availability of Jobs: Lets just assume we have jobs available in tons b. Pay scale for such jobs which do not require advanced degrees: lets assume each such available job pays you USD 40k/year in minimum
A college degree typically requires you to stick to college for 4 years. So in these 4 years, you will be sacrificing around USD 160k in total. This is the opportunity cost of going to college. However, this assumption can fail if jobs are not available and takes time to find as well your growth prospect in terms of career growth can be hindered by not having a college degree.