When K is the thermal conductivity, $$\tau$$ is the density and $$C_p$$, is the specific heat of a substance, then thermaldiffusivity is given by

A

$$\frac{K}{\tau.C_p}$$

B

$$\frac{K.C_p}{\tau}$$

C

$$\frac{\tau.C_p}{K}$$

D

$$\frac{K.\tau}{C_p}$$