Qu$$stion $41$

What is a foreign key?

a$.$ A foreign key is a primary key of a relation which is an attribute in another relation

b$.$ A foreign key is a superkey of a relation which is an attribute in more than one other relations

c$.$ A foreign key is an attribute of a relation that is a primary key of another relation

d$.$ A foreign key is the primary key of a relation that does not occur anywhere else in the schema