A) The invariants of the stress tensor: a) do not vary at varying reference system; b) take different values at varying reference system; c) coincide with the invariants of the strain tensor. B) The neutral axis in biaxial bending: a) never cuts the section; b) is a line passing through the centroid of the section; c) is a line tangent to the section. C) The nucleus of inertia: a) is always a polygon; b) is the region containing all the centers of pressures for which the section undergoes compression and tension in some points; c) is the region containing all the centers of pressures for which the section undergoes biaxial bending.

A) The invariants of the stress tensor: a) do not vary at varying reference system; b) take different values at varying reference system; c) coincide with the invariants of the strain tensor. B) The neutral axis in biaxial bending: a) never cuts the section; b) is a line passing through the centroid of the section; c) is a line tangent to the section. C) The nucleus of inertia: a) is always a polygon; b) is the region containing all the centers of pressures for which the section undergoes compression and tension in some points; c) is the region containing all the centers of pressures for which the section undergoes biaxial bending.