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
Function of a microtubule is/are: 
Select and explain. 
A. Strength of cell skeleton, B. Base for cilia arising from the cell, C. Movements of cytoplasm within the cell, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: None