Que. 
Given a Relation POSITION (PostingNo, Skill), then query to retrieve all distinct pairs of postingnos requiring skill is

a. 
Select p.postingNo, p.postingNo from position p where p.skill = p.skill and p.postingNo < p.postingNo 
b. 
Select p1.postingNo, p2.postingNo from position p1, position p2 where p1.skill = p2.skill 
c. 
Select p1.postingNo, p2.postingNo from position p1, position p2 where p1.skill = p2.skill and p1.postingNo < p2.postingNo 
d. 
Select p1.postingNo, p2.postingNo from position p1, position p2 where p1.skill = p2.skill and p1.postingNo = p2.posting.No 

Answer:Select p1.postingNo, p2.postingNo from position p1, position p2 where p1.skill = p2.skill and p1.postingNo < p2.postingNo 