A uniform rod of mass m, length L, area of cross-section A and Young's modulus Y hangs from a rigid support. Its  elongation due to its own weight will be:

• A

  $\frac{\mathrm{mgL}}{\mathrm{AY}}$

• B

  $\frac{\mathrm{mgL}}{2\mathrm{AY}}$

• C

  $\frac{3\mathrm{mgL}}{\mathrm{AY}}$

• D

  zero