This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optics and Errors of Refraction, Subject name: Ophthalmology
What is the angle subtended on each letter of the snellen's cha? 
Select and explain. 
A. 5 degrees, B. 10 degrees, C. 5 minutes, D. 10 minutes
C: 5 minutes
Answer: C: 5 minutes 
Explanation: Visual acuity test-types consist of a series of letters arranged in lines, each diminishing in size. The breadth of the lines of which the letters are composed is such that the edges will subtend an angle of 1 minute at the nodal point of the eye at a paicular distance. Each letter is shaped such that it can be placed in a square, the sides of which are five times the breadth of the constituent lines. Hence the whole letter will subtend an angle of 5 minutes at the nodal point of the eye at the given distance.