[Q]: How does the sentence end?

Dennis was less impressed with the crystals than Jason, because 

[A]: Dennis was seeing the crystals for the tenth time.


[Q]: How does the sentence end?

The ball smashed through the glass while the rock bounced off, since the 

[A]: ball was an effective missile.


[Q]: How does the sentence end?

Matthew put copper insulation in their pipes while Robert didn't, so 

[A]:
Robert 's pipe were dirty.