A rubber cord 10 m long is suspended vertically. How much does it stretch under its own weight (Density of rubber is 1500 kg/m³, $\left.\mathrm{Y}=5\times {10}^8\mathrm{N}/{\mathrm{m}}^2,\mathrm{g}=10\mathrm{m}/{\mathrm{s}}^2\right).$

• A

  $15\times {10}^{-4}\mathrm{m}$

• B

  $7.5\times {10}^{-4}\mathrm{m}$

• C

  $12\times {10}^{-4}\mathrm{m}$

• D

  $25\times {10}^{-4}\mathrm{m}$