Composite primary keys are particularly useful as identifiers of composite entities, where each primary key combination is allowed only once in the relationship.

M:N is the correct answer of this question.

Explanation:

M:N relationship is known as many to many relationship.

There is a many-to-many relationship when numerous data in a table are connected to duplicate entries from another table.The multiple-to-many relation is typically a duplicate of the true-life association between entities represented by the two or more  tables.

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