To recognize users across different devices, you must enable User ID feature.
- Attribution Models
- Audience Definitions
- AdWords Linking
- User ID
The correct answer is: User ID
Explanation:
The User ID lets you associate engagement data from multiple devices and different sessions with unique IDs. You must enable the User ID feature to recognize users across different devices.
Read more: https://support.google.com/analytics/answer/3123662