C is correct because transferring the user's existing account to Cloud Identity avoids conflicts and allows the user to retain their data while integrating with Cloud Identity. This method is recommended by Google for resolving account conflicts without losing access to existing data.

A is incorrect because using an email alias does not migrate the account to Cloud Identity, thus not resolving the conflict or enabling centralized management.

B is incorrect as deleting the account would remove the user's data, which is not necessary for conflict resolution.

D is incorrect because removing personal emails does not address the conflict issue and does not facilitate centralized account management.

For more information, refer to Google's documentation on migrating consumer accounts and resolving account conflicts.