In following formula which one indicates the least cost combination point

A. $${\text{MR}} = {\text{Me}}$$

B. $$\frac{{\Delta {\text{y}}}}{{\Delta {\text{x}}}}$$

C. $$\frac{{\Delta {{\text{y}}_1}}}{{\Delta {{\text{y}}_2}}}$$

D. $$\frac{{\Delta {{\text{x}}_2}}}{{\Delta {{\text{x}}_1}}} = \frac{{{\text{P}}{{\text{x}}_1}}}{{{\text{P}}{{\text{x}}_2}}}$$

Answer: Option D