Two concentric shells of masses M₁ and M₂ are having radii r₁ and r₂. Which of the following is the correct expression for the gravitational field at a distance r.
A. F=G (M₁+M₂)/ r₂forrB. F=GM₂/r₂ for r₁C. F=GM₁r₂ for r₁D. F=G(M₁+M₂) /r₂ for r