Two rods of different materials having coefficients of linear expansion a1 and a2 and Young's moduli, $Y_1$ and $Y_2$, respectively, are fixed between two rigid massive walls. The rods are heated such that they undergo the same increase in temperature. There is no bending of rods. If ${\alpha }_1$/${\alpha }_2$ = 2/3, then the thermal stresses developed in the two rods are equal, provided $Y_1$/$Y_2$ is equal to 

• A

  2 : 3 

• B

  1 : 1 

• C

  3 : 2 

• D

  4 : 9