Which of the following statements about functional dependencies is true?

a$.$ Column $B$ is functionally dependent on another column when a value for $B$ depends a single value for $A$ at any one time.

b$.$ Column $B$ is functionally dependent on another column when a value for $B$ determines a single value for $A$ at any one time.

c$.$ Column $B$ is functionally dependent on another column when a value for A determines a single value for B at any one time.

d$.$ Column B is functionally dependent on another column when a value for $B$ is part of $A.$