Thermal boundary layer thickness at the same location is

Question

For flow of fluid over a heated plate, the following fluid properties are known:

Viscosity = 0.001Pa.s; Specific heat at constant pressure = 1 kJ/kgK; Thermal conductivity = 1 W/mK;, The hydrodynamic boundary layer thickness at a specified location on the plate is 1mm, thermal boundary layer thickness at the same location is

      (a) 0.001mm                                                       (b) 0.01mm

      (c) 1mm                                                              (d) 1000 mm