A wide cylindrical tank with a small opening in the bottom has a water column of height `h_(1)` and above the water column, there is a layer of kerosene oil of thickness `h_(2). The velocity of efflux through the opening is
A. `sqrt(2gh_(1))`
B. `sqrt(2gh_(2))`
C. `sqrt(2g(h_(1)+h_(2)))`
D. Data is not sufficient.