r_12.4 is calculated as

A. $$\frac{{{{\text{r}}_{24}} - {{\text{r}}_{21}}\,{{\text{r}}_{14}}}}{{\sqrt {\left( {{\text{r}} - {\text{r}}_{12}^2} \right)\left( {1 - {\text{r}}_{11}^2} \right)} }}$$

B. $$\frac{{{{\text{r}}_{12}} + {{\text{r}}_{13}}\,{{\text{r}}_{24}}}}{{\sqrt {\left( {1 + {\text{r}}_{13}^2} \right)\left( {1 - {\text{r}}_{24}^2} \right)} }}$$

C. $$\frac{{{{\text{r}}_{13}} - {{\text{r}}_{12}}\,{{\text{r}}_{24}}}}{{\sqrt {\left( {1 + {\text{r}}_{12}^2} \right)\left( {1 - {\text{r}}_{24}^2} \right)} }}$$

D. $$\frac{{{{\text{r}}_{13}} - {{\text{r}}_{14}}{{\text{r}}_{24}}}}{{\sqrt {\left( {1 - {\text{r}}_{14}^2} \right)\left( {1 - {\text{r}}_{24}^2} \right)} }}$$

Answer: Option D