[Q]: How does the sentence end?

I tried to fit the paper under the door, but it wouldn't go because the 

[A]: door was too tight.


[Q]: How does the sentence end?

Talking to strangers and making friends came easily to Robert but not Michael because 

[A]: Michael was a prude.


[Q]: How does the sentence end?

The lung was infected after the surgery while the heart was still clean, since the tools used on the 

[A]:
lung were dirty.