Dmitri is waiting in line to receive a free t-shirt at a charity event. Because the shirts are free, there are many people in line, and a long wait time is expected. Consider the following sentence: By waiting in line for the shirt Dmitri will miss an appointment to tutor an economics student, for which he would have been paid $30. Which basic concept of individual choice does this sentence best illustrate

Opportunity cost and money cost are related but are not always exactly the same.

Explanation:

Opportunity costs may be defined as the costs which a person incurred when choosing the next best alternative  of the choices he or she has.

Money cost or the Nominal costs is nothing but the cost due to expenditure on something .

Here, in the context, the  opportunity cost is the cost of tution .

Money cost is zero as the good is free.

So both the costs are related with each other but are not always exactly the same

i would say b. research typically uses a variety of sources