A Sphere of Radius 'R1' Is Enclosed in a Sphere

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) 0
B) R² /(R1+R² )
C) 1
D) (R1/R² ) ²