Assertion (A): A database constraint can be added or removed any time in/from the database tables.

Reasoning (R): Alter table command is used to change the structure of the table.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Both A and R are true but R is not the correct explanation of A.

Explanation
A database constraint can be added or removed from database tables using the ALTER TABLE command, even after the table has already been created. This command is used to modify the structure of a table by altering the definition of its columns.