What is a true statement about Subscriber Key? (Choose 3)

orthern trail outfitters (NTO) is currently sending out a single welcome email when a subscriber join its myNTO rewards program. NTo wants to test whether one,two,three welcome emails would result in a higher rate of conversion.
How can this be accomplished most efficiently?

What are some of the acquisition methods to allow for subscribers to opt-in to receiving email? (Choose 3)

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 fed 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?

A marketer send an email to a send able data extension that contains a customer _ id fields with a numeric of data type that relates to the subscribers key and the all subscribers list as a send relationshipWhich two statements are correct about the emails send behavior for any subscribers who currently does not exist on the all subscribers list? Choose two answers