This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optics and refraction, Subject name: Ophthalmology
[{'content': "Jackson's cross cylinder test is used for - \nSelect and explain. \nA. Subjective verification, B. Subjective refining, C. Subjective balancing, D. Objective refining", 'role': 'user'}, {'content': "Answer: B \nExplanation: Jackson's crosscylinder test : It is used to verify the strength and axis of the cylinder prescribed. The crosscylinder is a combination of two cylinders of equal strength but with opposite sign placed with their axes at right angles to each other and mounted in a handle . The commonly used crosscylinders are of +-0.25 D and +-0.5 D. \x01 Verification of strength of the cylinder. Image: Jackson's cross cylinder Reference : A K KHURANA OPHTALMOLOGY,Edition 4,Page-555", 'role': 'assistant'}]