**Core Concept**
Surfactant plays a crucial role in reducing the surface tension within the lungs, thereby facilitating easier lung expansion during inhalation. This process is essential for maintaining normal lung mechanics and preventing atelectasis.

**Why the Correct Answer is Right**
The correct answer is related to the fact that surfactant production and secretion are accelerated by the hormone **cortisol**. Cortisol stimulates the production of surfactant proteins, particularly **SP-A and SP-D**, which are crucial for the formation and function of surfactant. This acceleration of surfactant production helps to reduce the surface tension within the lungs, making it easier to breathe.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because surfactant production is not accelerated by **adrenaline**. Adrenaline may actually have a negative effect on surfactant production in certain situations.

**Option B:** This option is incorrect because surfactant production is not accelerated by **growth hormone**. Growth hormone has various effects on the body, but accelerating surfactant production is not one of them.

**Option C:** This option is incorrect because surfactant production is not accelerated by **thyroid hormone**. While thyroid hormone has a wide range of effects on the body, it does not directly accelerate surfactant production.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that corticosteroids, such as **dexamethasone**, can accelerate surfactant production in preterm infants, which can help prevent respiratory distress syndrome (RDS) in this population.

**Correct Answer: D. Cortisol**