A plastic hemisphere has a radius of curvature of 8 cm and an index of refraction of 1.6. ON the axis halfway between the plane surface and the spherical one (4 cm from each) is a small object O. The distance between the two images when viewed along the axis from the two sides of the hemisphere is approximately
A. `1.0 cm`
B. `1.5 cm`
C. `3.75 cm`
D. `2.5 cm`