Least cost combination of inputs is achieved when

A. $$\frac{{\vartriangle {{\text{X}}_2}}}{{\vartriangle {{\text{X}}_1}}} > \frac{{{\text{P}}{{\text{X}}_1}}}{{{\text{P}}{{\text{X}}_2}}}$$

B. $$\frac{{\vartriangle {{\text{X}}_2}}}{{\vartriangle {{\text{X}}_1}}} < \frac{{{\text{P}}{{\text{X}}_1}}}{{{\text{P}}{{\text{X}}_2}}}$$

C. $$\frac{{\vartriangle {{\text{X}}_1}}}{{\vartriangle {{\text{X}}_2}}} = \frac{{{\text{P}}{{\text{X}}_1}}}{{{\text{P}}{{\text{X}}_2}}}$$

D. $$\frac{{\vartriangle {{\text{X}}_2}}}{{\vartriangle {{\text{X}}_1}}} = \frac{{{\text{P}}{{\text{X}}_1}}}{{{\text{P}}{{\text{X}}_2}}}$$

Answer: Option D