The correct answer is B) Selecting spare parts suppliers on the basis of reputation for quality. Selecting spare parts suppliers based on their reputation for quality is an effective way to reduce the frequency of required overhauls for machinery. High-quality spare parts are less likely to fail prematurely, which can extend the time between overhauls and reduce maintenance costs. In contrast, options A, C, and D (warranty policy, cost, and delivery time) are not directly related to the quality and durability of the spare parts, and would not have as significant an impact on reducing overhaul frequency.