Which of the following statements is correct ? (1) There are two types of stress, normal stress( σ ) and shear stress( τ ). (2) On one section, the normal stress( σ ) and the shear stress( τ ) must be perpendicular to each other. (3) On one section, all the normal stress( σ ) must be equal in size and same in the direction. (4) On one section, all the shear stress( τ ) must be parallel.