A concave lens of glass, refractive index 1.5 has both surfaces of same radius of curvature R . On immersion in a medium of refractive index 1.75, it will behave as a
a. convergent lens of focal length 3.5R
b. convergent lens of focal length 3.0R
c. divergent lens of focal length 3.5R
d. divergent lens of focal length 3.0R