The correct answer is A because Amazon Macie is a fully managed data security and privacy service that uses machine learning to automatically detect sensitive data such as PII (personally identifiable information) in Amazon S3. It requires no custom development, and it can be configured to generate alerts when sensitive data is detected in newly uploaded objects.

From AWS documentation:

"Amazon Macie automatically discovers and classifies sensitive data in S3 buckets and generates alerts when it detects sensitive content, such as names, addresses, and credit card numbers."

Explanation of other options:

B. Deploying an LLM on SageMaker to perform redaction is custom and operationally intensive.

C. Regex-based detection is brittle and requires extensive manual work, with high maintenance overhead.

D. Asking customers to avoid sharing sensitive data is not enforceable and does not meet compliance or security standards.

Referenced AWS AI/ML Documents and Study Guides:

Amazon Macie Documentation – Sensitive Data Discovery and Alerting

AWS Security Best Practices – Data Privacy and Governance

AWS ML Specialty Guide – Governance and Compliance Automation