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: Ophthalmology
Function of superior oblique muscle: 
Select and explain. 
A. Intoion, B. Extoion, C. Lateral rotation, D. Upward rotation
A: Intoion
Answer: A: Intoion 
Explanation: A i.e. Intoion