The cross sections of two hollow bars made of the same material are concentric circles as shown in the figure. It is given that $r_3>r_1$ and $r_4 > r_2$, and that the areas of the cross-sections are the same. $J_1$ and $J_2$ are the torsional rigidities of the bars on the left and right, respectively. The ratio $\displaystyle{\frac{J_2}{J_1}}$ is
- $>1$
- $<0.5$
- $=1$
- between $0.5$ and $1$