A ball rolls off to the top of a staircase with a horizontal velocity u m/s. If the steps are h meter high and b meter wide, the ball will hit the edge of the nth step, if

• A. \[n=\frac{2hu}{g{{b}^{2}}}\] 
• B.        \[n=\frac{2h{{u}^{2}}}{gb}\]
• C. \[n=\frac{2h{{u}^{2}}}{g{{b}^{2}}}\]          
• D.        \[n=\frac{h{{u}^{2}}}{g{{b}^{2}}}\]