A vessel of depth 2d cm is half filled with a liquid of refractive index `mu_(1)` and the upper half with a liquid of refractive index `mu_(2)`. The apparent depth of the vessel seen perpendicularly is
A. `d((mu_(1)mu_(2))/(mu_(1)+mu_(2)))`
B. `d(1/(mu_(1))+1/(mu_(2)))`
C. `2d(1/(mu_(1))+1/(mu_(2)))`
D. `2d(1/(mu_(1)mu_(2)))`