A sphere of radius 'R₁' is enclosed in a sphere of radius 'R₂'. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is

A. public class Circle implements Shape { private int radius; }B. public abstract class Circle extends Shape { private int radius; }C. public class Circle extends Shape { private int radius; public void draw(); }D. public abstract class Circle implements Shape { private int radius; public void draw(); }E. public class Circle extends Shape { private int radius; public void draw() { /* code here */ } }F. public abstract class Circle implements Shape { private int radius; public void draw() { /* code here */ } }