Your company has defined a set of S3 buckets in AWS. They need to monitor the S3 buckets and know the source IP address and the person who make requests to the S3 bucket. How can this be achieved?

Answer options:

A.Enable VPC flow logs to know the source IP addresses.
B.Monitor the S3 API calls by using CloudTrail logging.
C.Monitor the S3 API calls by using CloudWatch logging.
D.Monitor the S3 API calls by S3 object-level logging.

Answer: B
The AWS Documentation mentions the following.
Amazon S3 is integrated with AWS CloudTrail. CloudTrail is a service that captures specific API calls made to Amazon S3 from your AWS account and delivers the log files to an Amazon S3 bucket that you specify. It captures API calls made from the Amazon S3 console or from the Amazon S3 API.
Using the information collected by CloudTrail, you can determine what request was made to Amazon S3, the source IP address from which the request was made, who made the request, when it was made, and so on.
Options A and C are incorrect because these services cannot be used to get the source IP address of the calls to S3 buckets.
Option D is incorrect because there is no need to record the object-level API activity in the S3 bucket. Alternatively, you can use S3 server access logging to get the required information.
For more information on CloudTrail logging, please refer to the below Link:
https://docs.aws.amazon.com/AmazonS3/latest/dev/cloudtrail-logging.html