The correct answer is: B. Both, implicit and explicit cost.
Explicit costs are the monetary payments that a firm makes to acquire the inputs it needs to produce its output. Implicit costs are the opportunity costs of using resources that the firm already owns. For example, if a firm owns its own factory, the implicit cost of using the factory is the rent that the firm could have earned if it had rented the factory to another firm.
Both explicit and implicit costs are included in the economic cost of input. The economic cost of input is the total cost of using an input, including both the monetary payments made to acquire the input and the opportunity costs of using the input.
Option A is incorrect because it only includes explicit costs. Option C is incorrect because it only includes implicit costs. Option D is incorrect because both explicit and implicit costs are included in the economic cost of input.