(A) Google Tag Manager
(B) Sign-in that generates and sets unique IDs
(C) A new Analytics account for reporting
(D) All of the above
Google Analytics can recognise users across different devices through a login(Sign-in) authentication system that uses the User ID feature. This User ID feature allows you to associate a user with a unique identifier that can be used to track that user even if he/she logs in to your website using different devices. To make this happen, you need to create a login system where they input their username and password. This will allow the system to put a unique ID to that user and when he/she logs into your website using a different device but with the same account details then Google Analytics can recognize the user using that ID.
This question is a part of the Google Analytics Individual Qualification. You can get all the answers with detailed explanation for this exam in our Google Analytics Individual Qualification Exam Answers page.