A. To define the data structures
B. To specify the syntax and semantics of SQL data definition language
C. To specify the syntax and semantics of SQL manipulation language
D. All of the above.
Option D is the correct answer.
SQL is a query language designed for managing data held in a RDBMS, or for stream processing in a relational database management system (RDBMS).
If you want to learn SQL, check out this SQL Course by Intellipaat.