For Which of These Relationships Does an Efficient Relational Implementation

Multiple Choice

For which of these relationships does an efficient relational implementation of relationship AB require posting a foreign key? (in other words, for which relationship(s) would you always post a foreign key instead of making a separate table)

A) JK only
B) JK and PQ only
C) PQ only
D) YZ only
E) JK, PQ, and YZ