A thick cylindrical shell having r_o and r_i as outer and inner radii, is subjected to an internal pressure (p). The maximum tangential stress at the inner surface of the shell is

A. $$\frac{{{\text{r}}_{\text{o}}^2 - {\text{r}}_{\text{i}}^2}}{{2{\text{pr}}_{\text{i}}^2}}$$

B. $$\frac{{2{\text{pr}}_{\text{i}}^{\text{2}}}}{{{\text{r}}_{\text{o}}^2 - {\text{r}}_{\text{i}}^2}}$$

C. $$\frac{{{\text{p}}\left( {{\text{r}}_{\text{o}}^2 + {\text{r}}_{\text{i}}^2} \right)}}{{{\text{r}}_{\text{o}}^2 - {\text{r}}_{\text{i}}^2}}$$

D. $$\frac{{{\text{p}}\left( {{\text{r}}_{\text{o}}^2 - {\text{r}}_{\text{i}}^2} \right)}}{{{\text{r}}_{\text{o}}^2 + {\text{r}}_{\text{i}}^2}}$$

Answer: Option C