Two prismatic rods of identical lengths are designed for the same strain energy density when subjected to the same axial load. One of the rods is made of steel (Young's modulus $=210 \mathrm{GPa}$ ) and another is made of aluminum (Young's modulus $=70 \mathrm{GPa}$).
If the diameter of the aluminum rod is $70$ $\mathrm{mm}$, then which one of the following options corresponds to the diameter of the steel rod in mm?
- $53.19$
- $70$
- $210$
- $29.13$
