Answer:
b. foreign key
Explanation:
In the database world, a foreign key is a field on one table and a primary key for another table. The purpose of a foreign key is to provide linkages between two or more tables. Given two tables A and B, and making A the point of reference, a primary key is a field that is unique in A while a foreign key is unique in B.
On another hand, a composite primary key is a combination of two or more fields/columns on database table that can be used to uniquely identify each row in the table.
In the database lingua, what we have is a unique key not a distinct key, though the two words are similar in meaning.
A duplicate key is used when an information may be repeatedly entered on a table.
So the correct option is a foreign key.
