A marketer is configuring Path Optimizer in Journey Builder to test three different email subject lines. They want to configure a holdback audience to receive the winning path, but the option is unavailable.
Why would the marketer be unable to configure a holdback audience?

Northern Trail Outfitters has a list of Platinum members containing 50,000 subscribers and a Lifetime Member list containing 20,000 subscribers; 7,000 subscribers in the Lifetime Member list also exist in the Platinum Member list.
An email was deployed to the Platinum members, but the marketing team would now like to send the same email to the Lifetime Member list.
Which feature should be used when sending the second email to ensure that the 7,000 subscribers that exist on both lists don't receive the same email twice?

How can AMPscript customize email messages?

While testing an email with dynamic content in Content Builder, proofs of five content variations need to be reviewed directly in the inbox of a marketer's quality assurance specialist and the marketing manager. A data extension named 'myTestData' contains only the variations needed.
Which method should be used?

Northern Trail Outfitters (NTO) offers a 90-day trial on weekly snack box subscriptions. NTO would like to send out a series of emails to educate and remind members to purchase the subscription before the trial ends.
What tool is an option for this scenario?