Option A is correct because IAM roles are used to grant permissions to AWS services, such as EC2 instances, to access other AWS services, such as S3 buckets. The policy assigned to the IAM role attached to the EC2 instances should be checked to ensure that it grants access to the S3 bucket. Option B is also correct because the S3 bucket policy controls access to the S3 bucket. The S3 bucket policy should be checked to ensure that access permissions are correctly configured.