Q: To track users and sessions across multiple domains, what first must be set up?
A) Ad Exchange Linking
B) Data Import
C) AdWords Linking
D) Cross-domain tracking
Correct Answer is D) Cross-domain tracking.
When you set up cross domain tracking, you can collect data from multiple websites into a single account property. This lets you see data from different sites in the same reporting view.
Read more here: https://support.google.com/analytics/answer/1034148