To remove duplicate rows from the results of an SQL SELECT statement, the ________ qualifier specified must be included.

Answer: Option C

Option A: ONLY - The keyword ONLY is not used to remove duplicate rows in SQL SELECT statements. This option is incorrect.
Option B: UNIQUE - The UNIQUE keyword is not used in SQL SELECT statements to remove duplicate rows from results. It is used in table definitions for column uniqueness constraints. This option is incorrect.
Option C: DISTINCT - This option is correct. The DISTINCT qualifier in SQL SELECT statements is used to eliminate duplicate rows from the result set, returning only unique rows based on the specified columns.
Option D: SINGLE - The keyword SINGLE is not used in SQL SELECT statements to remove duplicate rows. This option is incorrect.
Conclusion:
To remove duplicate rows from the results of an SQL SELECT statement, you use the Option C: DISTINCT qualifier. Therefore, the correct answer is DISTINCT