What types of data can key fields in tables contain?

Key fields in tables are essential for uniquely identifying records within a dataset, and they must be of specific data types that adequately support this functionality. The correct option highlights the data types that can be effectively utilized as key fields in tables.

String is a versatile data type that can represent alphanumeric characters, making it suitable for labels, names, or other unique identifiers. Date is also a crucial type, allowing for the storage of temporal information which can be uniquely identified in scenarios involving timestamps or specific events. Reference, on the other hand, allows for the establishment of relationships among different tables or datasets by linking to entries in another table.

Choosing string, reference, and date as key field types ensures a robust mechanism for unique identification and relationship mapping within tables, which is critical in database design and management. The alignment of these data types allows for efficient querying and data integrity, making it essential for effective data handling in any application that employs relational databases or similar data structures.