**Core Concept**
Laryngomalacia is a congenital softening of the laryngeal cartilages, particularly the supraglottic area, which can lead to partial airway obstruction during inspiration. This condition is the most common cause of stridor in infants.

**Why the Correct Answer is Right**
Laryngomalacia is caused by the softening of the arytenoid cartilages and the anterior commissure, leading to an inward collapse of the supraglottic airway during inspiration. This results in a partial obstruction of the airway, causing the characteristic stridor. The severity of laryngomalacia can vary, but in most cases, it is a self-limiting condition that resolves on its own by 12-18 months of age.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because laryngomalacia is not typically associated with a bony anomaly or a congenital tracheal stenosis.

**Option B:** This option is incorrect because laryngomalacia is not usually caused by a mass or a tumor in the larynx.

**Option C:** This option is incorrect because laryngomalacia is not typically associated with a significant increase in the size of the larynx.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of laryngomalacia is the presence of inspiratory stridor, which is often more pronounced when the infant is agitated or crying. This is because the increased respiratory rate and effort can exacerbate the airway obstruction.

**Correct Answer: A. B. C.**