[Q]: How does the sentence end?

Donald but not Jason flipped through the catalog with ease because

[A]: Donald had great eyesight.

[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?

Donald ended the relationship against the wishes of Adam, because

[A]:
Adam wanted to be together.