The equation given by Coulomb for shear strength (s) of a soil at a point on a particular plane expressed as a linear function of the normal stress on that plane is ______________ (where c is cohesion and $$\Box$$ is angle of internal friction).

A

$$s = (\sigma + c) \tan \Box$$

B

$$s = (c + \sigma) \tan \Box$$

C

$$s = \sigma + c \tan \Box$$

D

$$s = c + \sigma \tan \Box$$