A child stands on the edge of the cliff 10 m above the ground and throws a stone horizontally with an initial speed of $$5 \text{ m s}^{-1}$$. Neglecting the air resistance, the speed with which the stone hits the ground will be ______ $$\text{m s}^{-1}$$ (given, $$g = 10 \text{ m s}^{-2}$$).

A

20

B

15

C

30

D

25