To answer this question, you need to understand the concept of trigger timing in database systems.
In Oracle, trigger timing refers to when a trigger is fired during the execution of a SQL statement. There are two types of trigger timing: statement-level and row-level.
Statement-level triggers are fired once for each triggering statement, regardless of the number of rows affected by the statement. These triggers do not have access to the individual rows that were affected by the statement. Therefore, you cannot reference the NEW and OLD qualifiers in statement-level triggers.
On the other hand, row-level triggers are fired once for each affected row within the triggering statement. These triggers have access to the individual rows that were affected by the statement. In row-level triggers, you can reference the NEW and OLD qualifiers to access the new and old values of the affected rows.
Based on this information, the correct answer is:
C. Row only - This option is correct because you can reference the NEW and OLD qualifiers in row-level triggers, but not in statement-level triggers.