Two pipe lines at a different pressures, $$p_A$$ and $$p_B,$$ each carrying the same liquid of specific gravity $$S_1$$ are connected to a U tube with a liquid of specific gravity of $$S_2$$ resulting in the level differences $$h_1, h_2 and h_3$$ as shown in the figure. The difference in pressure head between points A and B in terms of head of water is

A

$$h_1 S_2 + h_2 S_1 + h_3 S_1$$

B

$$h_1 S_1 + h_2 S_2 - h_3 S_1$$

C

$$h_1 S_1 - h_2 S_2 - h_3 S_1$$

D

$$h_1 S_1 + h_2 S_2 + h_3 S_1$$