[Q]: How does the sentence end?

During school the instructor taught the class using chalk but not marker because the 

[A]: marker was too expensive.


[Q]: How does the sentence end?

Brian showed Donald how to prepare glycerol stock since 

[A]: Donald had never made it before.


[Q]: How does the sentence end?

Wanting to become a forklift driver, Brett turns to Eric since 

[A]:
Eric can give a few lessons.