**Core Concept**
Stridor in adults is a high-pitched sound resulting from obstruction of the upper airway. The underlying cause can be anatomical, pathological, or iatrogenic. **Upper airway obstruction** is a medical emergency requiring prompt diagnosis and treatment.

**Why the Correct Answer is Right**
Since the correct answer is not provided, let's discuss a common cause of stridor in adults. A common cause is **foreign body aspiration**, which can lead to mechanical obstruction of the airway. Other causes include **laryngospasm**, **epiglottitis**, and **tumors**.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific option, it's difficult to provide a detailed explanation. However, if Option A is "asthma", it's incorrect because asthma typically causes wheezing, not stridor.
**Option B:** If Option B is "chronic obstructive pulmonary disease (COPD)", it's incorrect because COPD causes a chronic cough and shortness of breath, but not typically stridor.
**Option C:** If Option C is "pneumonia", it's incorrect because pneumonia causes symptoms like fever, cough, and shortness of breath, but not typically stridor.
**Option D:** Without the specific option, it's difficult to provide a detailed explanation.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that stridor is a symptom of upper airway obstruction, which can be life-threatening if not treated promptly.

**Correct Answer:** Not provided.