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 Members. Which field on the he Mountain Manor Campaign Data Extension should be created as the Primary Key to create a unique relationship with the Loyalty Member Profile Data Extension?