To answer this question, the user needs to have a basic understanding of SQL triggers and the difference between row level and statement level triggers.

The OLD and NEW qualifiers are used in row level DML triggers. These qualifiers refer to the old and new values of the row being modified by the DML statement.

A row level trigger is executed once for every row affected by the triggering DML statement. This means that if a DML statement modifies multiple rows, the row level trigger will be executed multiple times, once for each affected row.

Option A is correct because row level DML triggers are the only type of trigger that can use the OLD and NEW qualifiers to reference the old and new values of the row being modified.

Option B is incorrect because row level system triggers do not use the OLD and NEW qualifiers. System triggers are used to perform administrative tasks related to the database system, such as logging database activity.

Option C is incorrect because statement level DML triggers do not use the OLD and NEW qualifiers. Statement level triggers are executed once for each triggering DML statement, rather than once for each affected row.

Option D is incorrect because row level application triggers do not exist.

Therefore, the answer is: A. Row level DML trigger.