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
[{'content': 'While performing subjective verification of refraction, the cross cylinder is used to check: \nSelect and explain. \nA. Axis of the cylinder to be prescribed, B. Power of the cylinder to be prescribed, C. Both of the above, D. None of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. Both of the above', 'role': 'assistant'}]