‘Two plane slabs of equal areas and conductivities in the ratio 1 : 2 are held together and temperature in between surface ends are $$t_1$$ and $$t_2$$. If junction temperature in between two surfaces is desired to be $$\frac{t_1 + t_2}{2}$$, then their thicknesses should be in the ratio of

A

2 : 1

B

1 : 2

C

1 : 1

D

3 : 1