The default solution in Power Apps is the Common Data Service Default Solution, which is associated with the Microsoft Dataverse Default Publisher. The default publisher prefix will be randomly assigned for this publisher, for example it might be cr8a3. This means that the name of every new item of metadata created in the default solution will have this prepended to the names used to uniquely identify the items. If you create a new entity named Animal, the unique name used by Dataverse will be cr8a3_animal. The same is true for any new fields (attributes), relationships, or option-set options. If you'll be customizing this special solution, consider changing the publisher prefix.
Incorrect Answers:
A: You can only change the prefix of unmanaged solutions.
Reference:
https://docs.microsoft.com/en-us/power-platform/alm/use-solutions-for-your-customizations
https://docs.microsoft.com/en-us/powerapps/maker/data-platform/create-solution