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 foot-step 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 .