Two thin symmetrical lenses of different nature and of different material have equal radii of curvature `R = 15 cm`. The lenses are put close together and immersed in water `(mu_(w) = (4)/(3))`. The focal length of the system in water is 30 cm. The difference between refractive indices of the two lenses is

A. `(1)/(2)`

B. `(1)/(4)`

C. `(1)/(3)`

D. `(3)/(4)`