For a fluid having Prandtl number equal to unity, the relation between hydrodynamic boundary layer thickness ($$\delta_1$$) and thermal boundary layer thickness ($$\delta_2$$)

A

$$\delta_1 > \delta_2$$

B

$$\delta_1 < \delta_2$$

C

$$\delta_1 = \delta_2$$

D

$$\delta_2 = \frac{\delta_1}{3}$$