The demographics and interest category information in Google Analytics comes from:

• The Adwords first-party cookies
• Information that you upload from your CRM
• Survey data filled out by users
• The DoubleClick third-party cookie
• Google Tag Manager

The Correct Answer is:

•  The DoubleClick third-party cookie

Explanation: Demographics and Interests data comes from the third-party DoubleClick cookie (for web traffic) and from anonymous identifiers for mobile apps (i.e., Advertising ID for Android and IDFA for iOS). Neither analytics.js nor ga.js collects Demographics and Interests data.

You can read more here: https://support.google.com/analytics/answer/2799357?hl=en