A rubber cord 10 m long is suspended vertically. How much does it stretch under its own weight (Density of rubber is$1500\mathrm{kg}/{\mathrm{m}}^3$,$\left.\mathrm{Y}=5\times {10}^8\mathrm{N}/{\mathrm{m}}^2,\mathrm{g}=10\mathrm{m}/\mathrm{s}\right)$

• A

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

• B

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

• C

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

• D

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