Answer - (C)
Drop Primary Key.
We can not directly drop P.K. as
ALTER TABLE Table1
DROP PRIMARY KEY
Because it will show some kind of Error like,
Msg 156, Level 15, State 1, Line 3
Incorrect syntax near the keyword ‘PRIMARY’.
If we want to drop primary key constraint in SQL Server, run the following query.
ALTER TABLE Table1
DROP CONSTRAINT PK_Table1_Col1
Disabling Primary Key.
You can disable a primary key in Oracle using the ALTER TABLE statement.
Syntax
The syntax to disable a primary key using the ALTER TABLE statement in Oracle/PLSQL is:
ALTER TABLE table_name
DISABLE CONSTRAINT constraint_name;