The base of right pyramid is an equilateral triangle, each side of which is 20 cm . Each slant edge is 30 cm . The vertical height (in cm ) of the pyramid is:

A

$$\sqrt[10]{\frac{23}{3}}$$

B

$$\sqrt{3}$$

C

$$10\sqrt{3}$$

D

$$\sqrt[5]{\frac{23}{3}}$$