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)`