A bar of length l, breadth b and depth d is supported at its ends and is loaded at the centre by a load W. If Y is the Young's modulus of the material of the bar, then the depression $\mathrm{\delta }$ at the centre is

• A

  $\frac{{\mathrm{Wl}}^3}{4{\mathrm{bd}}^3\mathrm{Y}}$

• B

  $\frac{{\mathrm{Wb}}^3}{4{\mathrm{dl}}^3\mathrm{Y}}$

• C

  $\frac{{\mathrm{Wd}}^3}{4{\mathrm{lb}}^3\mathrm{Y}}$

• D

  $\frac{{\mathrm{Wl}}^3}{{\mathrm{bd}}^3\mathrm{Y}}$