A vertical shaft in a footstep bearing

Question

Consider the following statements:

1. Round bar in a round hole forms a turning pair.                   

2.   A square bar in a square hole forms a sliding pair.

3. A vertical shaft in a footstep bearing forms a successful constraint.

Which of these statements are correct?

         (a) 1 and 3            (b) 1 and 2  

         (c) 2 and 3            (d) 1, 2 and 3