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
Exocytosis 
Select and explain. 
A. Extrusion of cell bound vesicles, B. Intrusion of liquid particles, C. Instrusion of solid particles, D. All of the above
A: Extrusion of cell bound vesicles
Answer: A: Extrusion of cell bound vesicles 
Explanation: In exocytosis, the intracellular content to be released into the ECF fuses to the cell membrane. Then it is packed in a vesicle formed by the cell membrane and is released to the ECF.