The correct answer is: C. ALTER TRIGGER
The ALTER TRIGGER command is used to enable or disable a database trigger. To enable a trigger, use the ENABLE TRIGGER clause. To disable a trigger, use the DISABLE TRIGGER clause.
The MODIFY USER and CHANGE USER commands are used to change the user account of a database object. They are not used to enable or disable a database trigger.
For example, to enable the myTrigger trigger on the myTable table, you would use the following command:
ALTER TRIGGER myTrigger ON myTable ENABLE;
To disable the myTrigger trigger on the myTable table, you would use the following command:
ALTER TRIGGER myTrigger ON myTable DISABLE;