Which of the following scenarios best demonstrates a potential use of candidate keys in a relational database? 

Candidate keys in a relational database are columns or sets of columns that can uniquely identify records in a table and serve as potential primary keys. However, only one of them is chosen as the primary key, while the others remain as unique identifiers for backup or alternate purposes. For instance, in an employee database, both employee_id and social_security_number could be candidate keys, but only one is chosen as the primary key. The other remains a unique identifier, fulfilling the role of a candidate key. Candidate keys are essential in database design to ensure flexibility in record identification without data redundancy. They play a critical role in normalization by allowing tables to maintain unique records through various unique identifiers, ensuring data integrity and avoiding duplication. Option A - This option describes a scenario involving the selection of a primary key but does not capture the purpose of a candidate key, which exists as an alternative unique identifier. Option B - Foreign keys are used to create referential integrity by linking tables but are distinct from candidate keys, as they do not serve as unique identifiers within the original table. Option D - Composite keys, while related to unique identifiers, differ in function from candidate keys, as they are combinations of multiple fields that uniquely identify records. Option E - Normalization is achieved through functional dependencies and is not directly related to the role of candidate keys, which ensure uniqueness but are not involved in dependency elimination.