According to Nikuradse's the boundary behaves hydrodynamically smooth when

A

$$\left(\frac{k}{\delta}\right) > 10$$

B

$$\left(\frac{k}{\delta}\right) > 0.25$$

C

$$\left(\frac{k}{\delta}\right) < 0.25$$

D

$$\left(\frac{k}{\delta}\right) < 8$$