It is found that on walking x metres towards a chimney in a horizontal line through its base, the elevation of its top changes from 30° to 60° . The height of the chimney is

• A. $3\sqrt 2 \,x$$
• B. $2\sqrt 3 \,x$$
• C. $\frac{{\sqrt 3 }}{2}\,x$$
• D. $\frac{2}{{\sqrt 3 }}\,x$$