The question has multiple choices
a) Advanced filters
b) Cross-domain tracking
c) Event tracking
d) Custom Dimensions
The answer is b) Cross-domain tracking
Sometimes called site linking, this feature makes it possible for Google analytics to see sessions on two related websites as a single session by a single user. To track these sessions, Google analytics collects Client-Id value stored in cookies. In the case of multiple domains, the Client-Id value has to be carried from one domain to another.