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 are the objective tests of refraction ? 
Select and explain. 
A. Retinoscopy, B. Refractometry, C. Keratometry, D. All the above
D: All the above
Answer: D: All the above 
Explanation: Ans. is 'd' i.e., All the above