I get why D looks tempting since audit results are concrete, but maturity models (A) directly compare process levels to industry standards. That lets the CIO benchmark consistently. Pretty sure A is what they're looking for here unless it's about compliance specifically.
Pretty sure it's A for best way. Capability maturity models are designed for benchmarking process consistency, D is tempting but more about controls review not industry baselines. Feel free to disagree but that's what I've seen in other practice sets.