**Core Concept**
The presence of acute onset of cough, stridor, and respiratory distress in a pediatric patient, particularly in the absence of fever, points towards an obstruction or blockage of the airway. This condition is often caused by a foreign body that has been inhaled and is obstructing the airflow.

**Why the Correct Answer is Right**
A foreign body in the airway can cause an acute obstruction, leading to stridor (a high-pitched sound heard during inhalation) and coughing. The absence of fever suggests that this is not an infectious process. The location of the obstruction is typically in the upper airway, such as the trachea or bronchi. The presence of a foreign body can cause a complete blockage of the airway, leading to respiratory distress.

**Why Each Wrong Option is Incorrect**
**Option B:** Acute asthma is a condition characterized by airway inflammation and constriction, which typically presents with wheezing and shortness of breath. It is not typically associated with stridor or the acute onset of respiratory distress seen in foreign body aspiration.

**Option C:** Aspiration pneumonia refers to the inhalation of foreign material into the lungs, which can cause an infection. However, the absence of fever and the presence of stridor and cough suggest that this is not an infectious process.

**Option D:** Primary complex, also known as Ghon's complex, is a characteristic lesion seen in primary tuberculosis infection. It is not associated with the acute onset of respiratory distress or stridor.

**Clinical Pearl / High-Yield Fact**
When evaluating a pediatric patient with acute respiratory distress, it is essential to quickly assess for the presence of a foreign body in the airway. This can be done by performing a careful examination of the patient's mouth, nose, and throat, as well as by using a laryngoscope to visualize the airway.

**✓ Correct Answer: A. Foreign body**