Where should you define the workflow action?

Using Microsoft Visual Studio 2010, you create a custom workflow action named WF1 that copies
the content of a document library to another document library. WF1 is used in a Microsoft
SharePoint Designer reusable workflow. You need to ensure that the workflow action can be
deployed to multiple sites. Where should you define the workflow action?

A.
the SPPersistedObject object

B.
the WF1.actions file

C.
the ReplicatorActivity activity

D.
the Elements.xml file