Consider the following statements:
When a thick plate is subjected to external loads:
1. State of plane stress occurs at the surface
2. State of plane strain occurs at the surface
3. State of plane stress occurs in the interior part of the plate
4. State of plane strain occurs in the interior part of the plate
Which of these statements are correct?
(a) 1 and 3 (b) 2 and 4
(c) 1 and 4 (d) 2 and 3