Ans.) 4
Normal forms
Explanation: Functional dependency is a constraint that describes the relationship between attributes in a relation.
Data integrity refers to the accuracy and consistency of data stored in a database, data warehouse, data mart or other construct.
Referential integrity is a relational database concept, which states that table relationships must always be consistent.
Normalization is a process of organizing the data in database to avoid data redundancy, insertion anomaly, update anomaly & deletion anomaly. 1NF, 2NF, 3NF and BCNF are types of normal forms.
So, option (D) is correct.