Which query would achieve the required result?

Examine the structure of the PROMOTIONS table:
The management wants to see a report of unique promotion costs in each promotion category.
Which query would achieve the required result?

A.
SELECT DISTINCT promo_cost, promo_category FROM promotions;

B.
SELECT promo_category, DISTINCT promo_cost FROM promotions;

C.
SELECT DISTINCT promo_cost, DISTINCT promo_category FROM promotions;

D.
SELECT DISTINCT promo_category, promo_cost FROM promotions ORDER BY 1;