Exam AWS Certified SysOps Administrator - Associate topic 1 question 227 discussion

https://docs.aws.amazon.com/AmazonS3/latest/userguide/configuring-block-public-access-account.html

question asks "how to prohibit before exposure" not monitoring after exposure.

S3 Block Public Access is a security feature that can be enabled at the account level to prevent public access to S3 buckets and objects. It provides four settings for blocking public access, which can be applied at the account level, the bucket level, or the object level. By enabling this feature at the account level, all existing and future S3 buckets and objects will be protected against public access. This meets the requirement to prohibit the public exposure of any data in S3 buckets in the company's account.

Based on the 1st paragraph from this link: https://aws.amazon.com/s3/features/block-public-access/ it seems that A is the simplest solution.