• Access to YouTube masthead inventory
• Availability to frequency caps on all media buys across YouTube and other exchanges
• Access to Floodlight tag tracking without using dynamic pixels
• Access to earned metrics, like shares, and channel subscribers

The correct answer is: Access to earned metrics, like shares, and channel subscribers

Explanation: The linked Google Ads account can access reports from the YouTube channel including accessing additional video view statistics, call-to-action (CTA) overlays, and remarketing and engagement statistics such as earned views. If your Google Ads account is overseen by a manager account, linking your YouTube channel will allow the Google Ads manager account to access your YouTube channel metrics.

Read more here: https://support.google.com/youtube/answer/3063482