The correct answer is D. Change the existing CloudTrail trail so that it applies to all Regions.

According to the AWS documentation1, you can configure CloudTrail to deliver log files from multiple Regions to a single S3 bucket for a single account.To change an existing single-Region trail to log in all Regions, you must use the AWS CLI and add the --is-multi-region-trail option to the update-trail command2. This will ensure that you log global service events and capture all management event activity in your account.

Option A is incorrect because creating a new CloudTrail trail for each Region will incur additional costs and increase operational overhead. Option B is incorrect because changing the S3 bucket to receive notifications will not affect the delivery of log files from other Regions. Option C is incorrect because creating a new CloudTrail trail that applies to all Regions will result in duplicate log files for the original Region and also incur additional costs.