**Core Concept**
Montelukast is a leukotriene receptor antagonist used in the management of asthma and allergic rhinitis. It acts by inhibiting the action of leukotrienes, which are pro-inflammatory mediators involved in the pathogenesis of allergic diseases.

**Why the Correct Answer is Right**
Montelukast specifically targets the cysteinyl leukotriene receptor 1 (CysLT1R), a G-protein coupled receptor found on smooth muscle cells and other cells in the airways. By binding to this receptor, montelukast prevents the action of leukotrienes such as LTC4, LTD4, and LTE4, which cause bronchoconstriction, mucus production, and inflammation in the airways. This leads to improved lung function and reduced symptoms in patients with asthma and allergic rhinitis.

**Why Each Wrong Option is Incorrect**
**Option A:** Montelukast does not act by inhibiting the enzyme phospholipase A2, which is involved in the production of arachidonic acid and subsequent leukotriene synthesis.
**Option B:** Montelukast is not a corticosteroid, which is a different class of medication used to treat asthma and allergic diseases.
**Option C:** Montelukast does not act by increasing the levels of cyclic AMP (cAMP) in airway smooth muscle cells, which is a mechanism of action of beta-2 agonists.

**Clinical Pearl / High-Yield Fact**
Montelukast is a once-daily medication that can be used as an add-on therapy to inhaled corticosteroids in patients with asthma who require additional control of symptoms.

**Correct Answer: D. Inhibits the action of cysteinyl leukotrienes by binding to CysLT1R.**