Are constellations bound together by gravity?

No. There's no relationship among the stars in a constellation, and they're not bound together by anything. They may be many light years apart, and just happen to lie in roughly the same direction from the Earth so they appear close together as seen by US.

A constellation could be formed from the tree right in front of you, the cat in the grass next to the tree, and the house and two cars five miles away in the same direction as the tree.

They appear to form a pattern or a picture only because the human brain is hard-wired to look for familiar patterns in random stuff. The constellations exist only in our minds.

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.

the entire statement is true and correct.  

there's no diagram, nothing is illustrated, and no question is asked.