The coefficient of linear expansion of an in homogeneous rod changes linearly from α₁ to α₂ from one end to the other end of the rod. The effective coefficient of linear expansion of rod is

• A

  ${\mathrm{\alpha }}_1+{\mathrm{\alpha }}_2$

• B

  $\frac{{\mathrm{\alpha }}_1+{\mathrm{\alpha }}_2}{2}$

• C

  $\sqrt{{\mathrm{\alpha }}_1{\mathrm{\alpha }}_2}$

• D

  ${\mathrm{\alpha }}_1-{\mathrm{\alpha }}_2$