Northern Trail Outfitters (NTO) plans to launch an email campaign. They have two data extensions. The Mountain Manor Campaign data extension will contain the sending audience for this campaign and includes fields for Email Address, Full Name, Loyalty Member ID, and Loyalty Member Status. NTO will be using AMPscript to reference data in a second, nonsendable data extension named Loyalty Member.
Which field on the Mountain Manor Campaign data extension should be created as a Primary Key to create unique relationships with the Loyalty Member Profile data extension?