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
Most impoant factor for maintaining intravascular fluid volume - 
Select and explain. 
A. Hydrostatic pressure in capillaries, B. Osmotic pressure in capillaries, C. Hydrostatic pressure in interstitial space, D. Osmotic pressure in interstitial space
B: Osmotic pressure in capillaries
Answer: B: Osmotic pressure in capillaries 
Explanation: Ans. is 'b' i.e., Osmotic pressure in capillaries[Ref: Understanding medical physiology p. 331)Hydrostatic pressure in the capillaries, i.e., capillary blood pressure creates an outward driving force i.e., tries to force the fluid from the capillary to interstitial space.Osmotic pressure in the capillaries creates an inward driving force, ie., tries to keep the fluid in the capillary.