how many directions?

In a relational DBMS, a one-to-one relationship is said to have functional
dependence in how many directions?

A.
one

B.
two

C.
three

D.
four

E.
unlimited

Explanation:
A one-to-one relationship is said to have functional dependence in both
directions, because there will never be multiple values associated with a single value.
A one-to-many relationship has functional dependence in one direction, resembling
an algebraic function, and a many-to-many relationship has no functional
dependence.