**Core Concept**
Moderate exercise tachypnea refers to the increased respiratory rate observed during moderate-intensity physical activity. This phenomenon is primarily mediated by the autonomic nervous system, specifically the sympathetic division, which is activated in response to increased metabolic demands during exercise.

**Why the Correct Answer is Right**
The correct answer is related to the stimulation of chemoreceptors and mechanoreceptors in the lungs and chest wall, respectively. However, the primary mechanism underlying exercise-induced tachypnea is the stimulation of **J-receptors**, also known as pulmonary stretch receptors. These receptors are activated by the increased stretch and distension of the lungs during deep, rapid breathing, leading to an increase in parasympathetic tone and a subsequent decrease in sympathetic tone, resulting in an overall increase in respiratory rate.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the stimulation of **β2-adrenergic receptors** is primarily involved in bronchodilation and increased airflow during exercise, rather than the regulation of respiratory rate.
* **Option B:** This option is incorrect because the stimulation of **α-adrenergic receptors** is primarily involved in vasoconstriction and increased blood pressure during exercise, rather than the regulation of respiratory rate.
* **Option C:** This option is incorrect because the stimulation of **muscarinic receptors** is primarily involved in the regulation of smooth muscle tone and glandular secretion, rather than the regulation of respiratory rate during exercise.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that exercise-induced tachypnea is a normal physiological response to increased metabolic demands, and it's not a sign of respiratory disease unless it's accompanied by other abnormal respiratory symptoms or signs.

**Correct Answer:** D.