Final answer:
Assignment problems have an optimal solution where every changing cell has an optimal positive value.
Step-by-step explanation:
The correct answer for this question is D) Has an optimal positive value.
Assignment problems are mathematical models that involve a set of tasks and a set of agents. The goal is to assign agents to tasks in the most optimal way, based on certain criteria. The changing cells in an assignment problem typically represent the assignments made, and they can have different values based on the problem's context and constraints. In an optimal solution, these changing cells would have positive values that satisfy the problem's objective function and constraints.