Which one of the following relationships will provide least cost combination of input use?

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

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

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

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

Answer: Option A