The correct answer is C because enabling object versioning on the website's static data files in Google Cloud Storage ensures that the last known good version of the static content is always available for rollback. This method is seamless and efficient.

• Option A is incorrect because using Google Cloud Deployment Manager adds unnecessary overhead and could lead to conflicts between deployments, complicating the rollback process.
• Option B is incorrect as creating a Nearline copy is unreliable for keeping data in sync and does not provide a straightforward method for rolling back to a previous version once a bad update has been applied.
• Option D is incorrect because this approach does not scale well for frequent changes and involves significant management overhead.