Open pairs are those which have
A. Point or line contact between the two elements when in motion
B. Surface contact between the two elements when in motion
C. Elements of pairs not held together mechanically
D. Two elements that permit relative motion
Answer: Option C

Higher Pairs: point to point
Lower Pairs: surface to surface
Closed Pairs: Mechanical Arranged
Open Pairs: does not Arranged Mechanically
Kinematic Pairs: have relative motion