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
"Blow out " fracture of orbit involve -a) Floorb) Medial wallc) Lateral walld) Roofe) Apex 
Select and explain. 
A. ac, B. a, C. ad, D. ab
D: ab
Answer: D: ab 
Explanation: Blow out fracture involves :- i) Posterio-medial part of floor (most commonly), ii) Medial wall.