The correct answer is C. When an attempt is made to update the 'amt' column to NULL, it violates the constraint that the 'amt' column cannot be NULL. This action results in the SQL error SQL0407N, which states that assigning a NULL value to a column that is defined as NOT NULL is not allowed. Consequently, the row cannot be updated to (2, NULL), and the trigger does not take effect because the initial update statement itself fails due to the NOT NULL constraint violation.