Two identical particles are projected horizontally in opposite directions with a speed of \[5\text{ m}{{\text{s}}^{-1}}\] each from the top of a tall tower as shown. Assuming \[\text{g = 10 m}{{\text{s}}^{-2}}\], the distance between them at the moment when their velocity vectors become mutually perpendicular is

• A. 2.5 m               
• B. 5 m
• C. 10 m                            
• D. 20 m