Young's, shear and bulk moduli and Poisson's ratio describe how a solid deforms. Pick the option listing exactly the true claims among I to IV on their signs, sizes and dimensions.

• I. Poisson's ratio has neither unit nor dimensions.
• II. For most materials the shear modulus is about one-third of Young's modulus.
• III. The bulk modulus of a material is negative because its volume decreases when pressure increases.
• IV. Stress has the same dimensional formula as pressure.