Final answer:
Management accountants add value in benchmarking by giving insights into why cost structures differ among firms, which aids in strategic decision-making. (option a)
Step-by-step explanation:
When benchmarking, management accountants are most valuable when a) they provide insight into why costs or revenues differ across companies. This effort goes beyond merely presenting or highlighting differences in the benchmarking data. By breaking down total costs into fixed cost, marginal cost, average total cost, and average variable cost, accountants offer valuable insights into the cost structure and performance of a firm compared to its peers in the industry. This breakdown is essential as each type of cost provides different insights that are crucial for strategic decision-making and improvement initiatives.