A stone is projected with a velocity `10sqrt(2)m/s^(-1)` at an angle of `45^(@)` to the horizontal ground.The average velocity of stone during its time of flight is `(A) 10m/s^(-1) (B) 10sqrt(5)m/s^(-1) (C) 5sqrt(5)m/s^(-1)(D) 20m/s ^(-1)`