In which case must you use a referencing relationship from entity type E1 to entity type E2? Please choose the correct answer.

In which case must you use a referencing relationship from entity type E1 to entity type E2? Please choose the correct answer.
A . Entity type E1 is of storage/use type 4
B . Entity type E2 is of storage/use type 1
C . Entity type E1 is an attribute of the entity type E2
D . Entity type E1 is part of the key of the entity type E2

Answer: C