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
In human body the action of surfactant is done by 
Select and explain. 
A. Sugar and salt, B. Soap and water, C. Lipid and protein, D. Base and lipid
C: Lipid and protein
Answer: C: Lipid and protein 
Explanation: None