What is System -> Design used for?

A.
Configuring the fallback system of a store view

B.
Overriding the fallback system of a store view for a limited period of time

C.
Activating the fallback system of a store view

D.
Overriding the fallback system of a subpart (Layout, Templates, …) of a store view

E.
Configuring basic Package and Theme settings of your Magento instance