Consider the following statements, in connection with a metallic rod of a circular section being subjected to equal and opposite torque T within elastic limit:
1. The transverse section of the rod does not experience warping.
2. The diameter of rod does not alter.
3. Angle of relative twist between two sections is proportional to the lengths between these sections.
4. A surface element of the rod is under pure shear state of stress.
Which of these statements are correct?
(a) 1, 2, 3 and 4 (b) 1, 2 and 3 only
(c) 2 and 3 only (d) 2, 3 and 4 only