Explanation
Einstein Messaging Insights provides notification badges to alert marketers of any performance issues with their email campaigns. It also provides recommendations on how to improve the email performance. [Source:
Trailhead]

Explanation
The email address has not been updated in All Subscribers is the correct answer. All Subscribers is the master list of subscribers in Marketing Cloud, and it stores the email address, subscriber key, and status for each subscriber. If a subscriber changes their email address, it needs to be updated in All Subscribers as well as in any other data extensions or lists that store the subscriber information. Otherwise, Marketing Cloud will still send emails to the old address stored in All Subscribers. You can learn more about this in the Manage Subscribers module on Trailhead.

Explanation
A query activity allows you to use SQL statements to retrieve data from data extensions and data views based on specific criteria. You can use a query activity to find the affected customers by using a date range parameter in your SQL statement

Explanation
Utilizing exit criteria for the journey is a way to simplify the journey that has a decision split prior to every email send to remove certain subscribers from the journey. Exit criteria can define when contacts should exit the journey based on specific conditions, such as unsubscribing or making a purchase. This will eliminate the need for multiple decision splits on the journey canvas. [Source: Trailhead]

Explanation
Contacts analytics is a report that shows how the cross-channel customer population has changed over time. It can be used to track the growth or decline of contacts across different channels, such as email, mobile, or social. Contacts count is a report that shows the total number of contacts in the account. Audience engagement over time is a report that shows how contacts interact with messages over time.