The correct answer is: B. Explicit
Explicit costs are costs that a firm incurs in order to produce its goods or services. These costs are directly paid out by the firm, such as wages paid to workers, rent paid for office space, and the cost of raw materials.
Implicit costs are costs that a firm incurs but does not directly pay out. These costs are the opportunity costs of using resources that the firm already owns, such as the opportunity cost of using the time of its owners.
Real costs are costs that are measured in terms of real goods and services. Nominal costs are costs that are measured in terms of money.
In the context of the question, the cost which a firm incurs for purchasing or hiring factors is an explicit cost. This is because the firm directly pays out money for these costs.