Two metallic blocks $$M_1$$ and $$M_2$$ of same area of cross-section are connected to each other (as shown in figure). If the thermal conductivity of $$M_2$$ is $$K$$ then the thermal conductivity of $$M_1$$ will be : [Assume steady state heat conduction]

A

$$10K$$

B

$$8K$$

C

$$12.5K$$

D

$$2K$$