The correct answer is: D. Opportunity cost
Opportunity cost is the cost of any activity measured in terms of the value of the next best alternative forgone. In other words, it is the cost of a choice that is made when one alternative is selected over another.
For example, if you choose to go to the movies, the opportunity cost is the value of the other things you could have done with that time, such as studying, working, or spending time with friends.
Production cost is the cost of producing a good or service. It includes the cost of labor, materials, and other inputs used in production.
Physical cost is the cost of something in terms of the physical resources that are used to produce it. For example, the physical cost of a car is the cost of the materials used to build it, such as steel, plastic, and rubber.
Real cost is the cost of something in terms of the goods and services that could have been purchased with the same amount of money. For example, the real cost of a college education is the amount of money that could have been earned if you had worked instead of going to college.