Solution of Laplacian equation in three dimensions $$\frac{{{{\text{d}}^2}\varphi }}{{{\text{d}}{{\text{x}}^2}}} + \frac{{{{\text{d}}^2}\varphi }}{{{\text{d}}{{\text{y}}^2}}} + \frac{{{{\text{d}}^2}\varphi }}{{{\text{d}}{{\text{z}}^2}}} = 0$$     of water in a syphon, is done by

A. Analytical method

B. Khosla's method

C. Method of relaxation

D. Unwin's method

Answer: Option C