The Young’s modulus of Brass and Steel are respectively $1.0\times {10}^{10}\mathrm{N}/{\mathrm{m}}^2\mathrm{and}2\times {10}^{10}\mathrm{N}/{\mathrm{m}}^2$. A Brass wire and a Steel wire of the same length are extended by 1mm under the same force, the radii of Brass and Steel wires are ${\mathrm{R}}_{\mathrm{B}}\mathrm{and}{\mathrm{R}}_{\mathrm{S}}$ respectively. Then

• A

  ${\mathrm{R}}_{\mathrm{S}}=\sqrt{2}{\mathrm{R}}_{\mathrm{B}}$

• B

  ${\mathrm{R}}_{\mathrm{S}}=\frac{{\mathrm{R}}_{\mathrm{B}}}{\sqrt{2}}$

• C

  ${\mathrm{R}}_{\mathrm{S}}=4{\mathrm{R}}_{\mathrm{B}}$

• D

  ${\mathrm{R}}_{\mathrm{S}}=\frac{{\mathrm{R}}_{\mathrm{B}}}{4}$