While solving an assignment problem, an activity is assigned to a resource through a square with zero opportunity cost because the objective is to?

While solving an assignment problem, an activity is assigned to a resource through a square with zero opportunity cost because the objective is to minimize total cost of assignment. The objective of assignment problem is to assign a number of jobs to an equal number of machines so as to minimize the total assignment cost or to minimize the total consumed time for execution of all the jobs. In the multi-objective assignment problem, the objectives alone are considered as fuzzy.