A fish is raising vertically to the surface of water in a lake uniformly at the rate of \[2m{{s}^{-1}}\] observes a bird diving vertically towards the water at a rate \[4m{{s}^{-1}}\] vertically above it. The refractive index of water is 4/3. The actual velocity of the bird is

• A.  3/2       
• B.  2/3    
• C.  4/3                       
• D.  3/4