The rods A and B are heated.If $\alpha_1 : \alpha_2=5 : 7$,the thermal stresses develpoed on the two rods are equal if $Y_1 : Y_2$ is

Question

$\begin{array}{1 1}(A)\;5 : 7\\(B)\;1 : 1\\(C)\;7 : 5\\(D)\;25 : 49\end{array} $