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
Which of the following is/ are contrast sensitivity testing chas? 
Select and explain. 
A. Pellirobsons, B. Snellen type cha, C. Regan cha, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Ans. is d i.e., All of the above Contrast Sensitivity Testing is done with the help of following chas: Pelli-Robson cha The Regan cha StandardSnellen-type