Which of the following choices best illustrates the concept of opportunity cost?

Opportunity cost refers to the value of the next best alternative that is foregone when making a decision. In this case, the scenario of spending time studying instead of working clearly demonstrates this concept. When you choose to study, you are sacrificing the potential income you could have earned from working during that same period. This lost income represents the opportunity cost of studying—it's the benefit you could have gained had you chosen to work instead.

The other options do not illustrate opportunity cost as effectively. The money spent on a new car reflects a direct expenditure but does not highlight the next best alternative that was forfeited. Tax payments are obligations that do not present an alternative choice in the same way studying versus working does. Finally, while physical resources used in production pertain to economic decisions, they do not directly capture the notion of opportunity cost, which is centered on the alternatives forgone in decision-making. Therefore, the situation that best encapsulates opportunity cost is indeed the time spent studying instead of working.