Which of the following is true of database querying?

A$.$ A primary key is used to provide a link between data in two tables, but a foreign key is designated to uniquely identify all table records.

B$.$ Normalization is used to simply data query, but denormalization can reduce the data redundancy.

C$.$ A database has various database models such as network model, hierarchical model, and relational model.

D$.$ SQL is the program used to create, process, and administer a database.