iI am stuck on this question, do you know the right answer for this

Question 3 In applying branch and bound technique to assign 4 jobs to 4 persons such that the total cost is minimum, and each person is assigned with exactly one job, which of the following statements correctly describe the nature of upper bound? Answer saved Marked out of 1.00 P Flag question Select one: O a. upper bound is the cost for an optimal but may not be feasible assignment O b. upper bound is the cost for a feasible but may not be optimal assignment O c. upper bound is neither the cost for a feasible assignment nor the cost for an optimal solution O d. upper bound is the cost for a feasible optimal assignment Clear my choice