The correct answer is C. 2.
A relation is an association between two or more entities. In a database, a relation is represented by a table. Each table has a set of columns, which represent the attributes of the entities, and a set of rows, which represent the instances of the entities.
The two relations that may exist between tables in databases are one-to-one and one-to-many.
A one-to-one relation is a relationship between two tables in which each row in the first table can only be associated with one row in the second table, and vice versa.
A one-to-many relation is a relationship between two tables in which each row in the first table can be associated with multiple rows in the second table, but each row in the second table can only be associated with one row in the first table.
For example, a table of customers and a table of orders may have a one-to-one relationship. Each customer can only have one order, and each order can only be placed by one customer.
A table of products and a table of orders may have a one-to-many relationship. Each product can be ordered multiple times, but each order can only contain one of each product.