This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
For pulmonary maturation, Which is required during gestation? 
Select and explain. 
A. Cortisol, B. Surfactant, C. Amniotic fluid, D. Acetylcholine
B: Surfactant
Answer: B: Surfactant 
Explanation: None