A block of wood with a cylindrical shape has cross-sectional area $A$ and weight $W$. It is completely submerged in water, with its axis in a vertical position. The pressures acting on its top and bottom faces are $p_t$ and $p_b$ respectively. Which expression gives the upthrust acting on the block?
- A$(p_b - p_t)$
- B$(p_b - p_t)A$
- C$(p_b - p_t)A - W$
- D$(p_b - p_t)A + W$