a concave lens of glass, refractive index 1.5, has both surface of same radius of curvature R. On immersion in a medium of refractive index 1.75, it will have 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.