Universal Containers (UC) is transitioning from Classic to Lightning Experience.

The correct answer is C, migrate Notes and Attachment to Enhanced Notes and Files using a migration tool. Enhanced Notes and Files are the new features in Lightning Experience that replace the classic Notes and Attachments. They offer more functionality and security than the classic version. To access them in Lightning Experience, you need to migrate your existing Notes and Attachments using a migration tool provided by Salesforce. Adding Notes and Attachments Related List, manually uploading Notes or Attachments, or doing nothing are not valid solutions, as they will not enable you to use the enhanced features in Lightning Experience.