The absolute pressure on dolphin when it is 5 m below the free surface of the water is

Question

When a dolphin glides through air, it experiences an external pressure of 0.75 m of mercury. The absolute pressure on dolphin when it is 5 m below the free surface of the water is           

(A) 0.10 N/mm²          (B) 0.5 N/mm²

 (C) 1.0 N/mm²            (D) 0.15 N/mm²