Which command(s) is(are) used to enable/disable/drop an integrity constraint in SQL?

The correct answer is C. ALTER TABLE.

The ALTER TABLE command is used to modify the structure of a table. This includes adding, removing, or changing columns, constraints, and indexes. To enable or disable an integrity constraint, you can use the ALTER TABLE command with the SET CONSTRAINT statement. To drop an integrity constraint, you can use the ALTER TABLE command with the DROP CONSTRAINT statement.

The DEFINE TABLE command is used to create a new table. It does not allow you to modify the structure of an existing table.

The MODIFY TABLE command is used to modify the data in a table. It does not allow you to modify the structure of a table.

Therefore, the only command that can be used to enable/disable/drop an integrity constraint is ALTER TABLE.