Q: To collect how many times users downloaded a product catalog, what would you set up ?
A) Custom Dimension
B) Custom Report
C) Calculated Metrics
D) Event Tracking
Correct Answer is D) Event Tracking.
Events are user interactions with content that can be tracked independently from a web page or a screen load. Downloads, mobile ad clicks, gadgets, Flash elements, AJAX embedded elements, and video plays are all examples of actions you might want to track as Events.
Read more here: https://support.google.com/analytics/answer/1033068