If A is the area of the foundation of a retaining wall carrying a load W and retaining earth of weight 'w' per unit volume, the minimum depth (h) of the foundation from the free surface of the earth, is

A. $${\text{h}} = \frac{{\text{W}}}{{{\text{Aw}}}}\left[ {\frac{{1 - \sin \varphi }}{{1 + \sin \varphi }}} \right]$$

B. $${\text{h}} = \frac{{\text{W}}}{{{\text{Aw}}}}\left[ {\frac{{1 + \sin \varphi }}{{1 - \sin \varphi }}} \right]$$

C. $${\text{h}} = \frac{{\text{W}}}{{{\text{Aw}}}}{\left[ {\frac{{1 - \sin \varphi }}{{1 + \sin \varphi }}} \right]^2}$$

D. $${\text{h}} = \sqrt {\frac{{\text{W}}}{{{\text{Aw}}}}} {\left[ {\frac{{1 - \sin \varphi }}{{1 + \sin \varphi }}} \right]^2}$$

Answer: Option C