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': 'Cross cylinders is \nSelect and explain. \nA. One plus cylinder and one minus cylinder of equal strength, B. One plus cylinder and one minus cylinder of unequal strength, C. Two plus cylinders, D. Both minus cylinders', 'role': 'user'}, {'content': "Answer: A \nExplanation: A i.e. One plus cylinder and one minus cylinder of equal strength Cross cylinder is a combination of two cylinders of equal strength but with opposite sign placed with their axis at right angles to each otherQ and mounted in a handle. Jackson's cross cylinder test is used to verify the strength & axis of the cylinder prescribed. The commonly used cross cylinders are of +- 0.25 D and -0.5 D.", 'role': 'assistant'}]