**Core Concept**
The 2nd phase of bronchial asthma, also known as the late phase or dual response, is a complex phenomenon involving the release of various chemical mediators, such as histamine, leukotrienes, and cytokines, from mast cells, eosinophils, and other inflammatory cells. This response is mediated by the recruitment of inflammatory cells to the airways and the release of pro-inflammatory cytokines.

**Why the Correct Answer is Right**
The 2nd phase of bronchial asthma can be prevented by using corticosteroids, which act by inhibiting the transcription of inflammatory genes and reducing the expression of pro-inflammatory cytokines. Corticosteroids also decrease the number of inflammatory cells in the airways and reduce the release of chemical mediators. This is achieved by suppressing the activation of nuclear factor kappa B (NF-κB), a key transcription factor involved in the regulation of inflammatory genes.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because bronchodilators, such as beta-2 agonists, only provide symptomatic relief by relaxing the smooth muscles of the airways, but do not affect the underlying inflammatory process.

**Option B:** This option is incorrect because antihistamines, such as diphenhydramine, only block the action of histamine, but do not address the broader inflammatory response involved in the 2nd phase of bronchial asthma.

**Option C:** This option is incorrect because leukotriene modifiers, such as montelukast, only inhibit the action of leukotrienes, but do not address the other chemical mediators involved in the 2nd phase of bronchial asthma.

**Clinical Pearl / High-Yield Fact**
Corticosteroids are the most effective treatment for preventing the 2nd phase of bronchial asthma, and their use should be initiated early in the course of the disease to prevent the development of persistent airway inflammation.

**Correct Answer:** C. Corticosteroids.