Which one of the following statements is true for Mohr-Coulomb envelope ?

• A. Coulomb suggests that the relationship between shear strength and normal stress, is adequately represented by the straight line
• B. The generalised Mohr theory suggests that, though the shear stress depends on the normal stress, the relation is not linear
• C. Coulomb and Mohr suggest that a definite relationship exists among the principal stress and the angle of internal friction
• D. All the above.