Comprehensive and Detailed 250 to 300 words of Explanation (AWS documentation-based, no links):

Amazon Macie is the AWS managed service specifically built to discover, classify, and protect sensitive data in Amazon S3, including many common types of personally identifiable information (PII). Macie uses automated analysis and machine learning to identify sensitive data patterns at scale and produces findings that can be reviewed, prioritized, and integrated into security workflows. Because the environment spans hundreds of buckets, millions of objects, and multiple Regions, the key requirement is to minimize operational overhead while achieving broad coverage.

Option C is therefore the best fit: enabling Macie and configuring it to evaluate the targeted buckets provides a centralized, managed approach without building custom scanners, maintaining parsing logic, or operating distributed processing pipelines. Macie is designed for large-scale S3 estates and reduces ongoing maintenance compared with bespoke solutions.

Option A is incorrect because Amazon Detective is used to investigate and analyze security findings and relationships, not to classify S3 object content for PII. Option B is incorrect because Trusted Advisor provides best-practice checks (cost, security posture items, limits), but it does not inspect S3 object contents to detect PII. Option D would require building and operating custom Lambda scanning across millions of objects, handling pagination, retries, file types, performance tuning, and cost controls—high operational overhead and ongoing maintenance, which the company wants to avoid.

Therefore, C meets the requirement most directly and with the least operational burden by using the AWS service purpose-built for PII discovery in S3.