Final answer:
Singulair is the respiratory medication from the list that is not a combination product, as it only contains montelukast.
Step-by-step explanation:
The respiratory medication that is not a combination product among the options provided is d. Singulair. While Advair contains a combination of fluticasone and salmeterol, and Combivent contains a combination of albuterol and ipratropium, Singulair is a single-ingredient medication with the active ingredient montelukast, which is used to prevent asthma attacks and to treat allergies. Allegra D, although not primarily a respiratory medication, is also a combination product containing fexofenadine and pseudoephedrine.
Singulair is a medication used to prevent asthma attacks and treat seasonal allergies. It contains the active ingredient montelukast, which is not combined with any other drug. On the other hand, Advair (a), Combivent (c), and Allegra D (b) are all combination products that contain multiple active ingredients to treat respiratory conditions.