What is a possible reason for the grayed out Restore Version button in the screenshot of the Database Revision Control while trying to restore Old_Structure?

What is a possible reason for the grayed out Restore Version button in the screenshot of the Database Revision Control while trying to restore Old_Structure?

A.
Old_Structure was not approved in SmartWorkflow.

B.
No SmartWorkflow session is started.

C.
With SmartWorkflow active, only SmartWorkflow revisions could be restored.

D.
Self-created versions cannot be restored if there are newer versions created in SmartWorkflow.