Primary and foreign key relationship

Can a developer manually define a primary and foreign key relationship between two columns in two different relational Source definitions?

Choose Answer

(A)
Yes, always.
(B)
Yes, provided that the data types and precision matches between the two columns.
(C)
Yes, provided that the data types and precision matches between the two columns and the relationship exists on the physical database tables when the session runs.
(D)
Yes, provided that the data types and precision matches between the two columns. The relationship can be set between the Source definitions regardless of whether the relationship exists on the physical database tables, but if the relationship does not exist in the database, the session may fail if referential integrity is faulty.