You can do this, but:
1) You can add reference to a property set that is unique.
2) As primary key, (A,B,C) is unique.
3) If you want to add reference to (A,B), it has to be unique
4) If (A,B) is unique thus a primary key candidate, why is (A,B,C) the primary key after all?
I smell a design problem. Please consult the following article too:
http://www.sqlmag.com/article/systems-administrator/sql-by-design-how-to-choose-a-primary-key-5113[
^]