Which one of the following is the opportunity cost of a chosen activit

Which one of the following is the opportunity cost of a chosen activity ?

Out of pocket cost
Out of pocket cost plus cost incurred by the Government
Value of all opportunities forgone
Value of next best alternative that is given up
This question was previously asked in
UPSC CDS-2 – 2021
Opportunity cost is the value of the next best alternative that must be forgone to pursue a certain action. It represents the benefits you could have received by taking an alternative action. When you choose one activity, you give up the opportunity to engage in other activities; the opportunity cost is the value of the single best option you did not choose.
Opportunity cost is the value of the next best alternative foregone.
It is distinct from explicit or ‘out-of-pocket’ costs (accounting costs). Economic decision-making often considers both explicit and implicit (opportunity) costs. For example, the opportunity cost of attending college includes not only tuition and books (explicit costs) but also the income you could have earned if you had worked instead of studying (implicit cost).