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
The Most convenient form of cross cylinder is a combination of - 
Select and explain. 
A. -0.5 Diopter sphere with +1 Diopter Cylinder, B. +0.5 Diopter sphere with -1 Diopter Cylinder, C. +0.25 Diopter sphere with -0.5 Diopter Cylinder, D. -0.25 Diopter sphere with +0.5 Diopter Cylinder
A: -0.5 Diopter sphere with +1 Diopter Cylinder
Answer: A: -0.5 Diopter sphere with +1 Diopter Cylinder 
Explanation: Jackson's cross cylinder 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 Image: Jackson's cross cylinder Reference : A K KHURANA OPHTALMOLOGY,Edition 4,Page-555