A boy projects a stone vertically perpendicular to the trolley car with a speed \[v\]. If the trolley car moves with \[u\]constant velocity m, the time of flight of the stone is:

• A. \[\frac{u+v}{g}\]         
• B. \[\frac{2v}{g}\]
• C. \[\frac{2u}{g}\]            
• D. none of these