"Treat source rows as" session property

A user sets the "Treat source rows as" session property to "Update". What is the effect of making this selection?

Choose Answer

(A)
All records processed by the session will be treated as update statements on the target table(s).
(B)
All records processed by the session will be treated as update statements on the target table(s), provided that a primary key constraint exists on the corresponding target table definition(s).
(C)
This selection allows the use of the Update Strategy transformation, provided that one or more Update Strategy transformations are present in the mapping run by the session.
(D)
This selection allows the use of the Update Strategy transformation, provided that one or more Update Strategy transformations are present in the mapping run by the session, and provided that a primary key constraint exists on the corresponding target table definition(s).