You need to delete the previous versions of all documents in a document library.

The deleted versions of the documents must be retained in the SharePoint Recycle Bin.

What should you do?

A.
For the document library, call the Recycle method.

B.
For the document library, call the Delete method.

C.
For each document, call the DeleteAll method of the Versions property.

D.
For each document, call the RecycleAll method of the Versions property.

Explanation:
MNEMONIC RULE: “all previous versions to Recycle Bin = RecycleAll of the Versions”

Recycles the version collection except for the current version.

SPListItemVersionCollection.RecycleAll Method
http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.splistitemversioncollection.recycleall.aspx