[Q]: How does the sentence end?

After Samantha finished putting nail polish on their daughter's nails, Natalie paid for the service; then

[A]: Natalie realized they forgot to leave a tip.

[Q]: How does the sentence end?

Jeffrey wanted Neil to do well on the SATs, since

[A]: Neil had the chance to college when they were young.

[Q]: How does the sentence end?

Lindsey loves the chocolate chip cookies that Megan makes because

[A]:
Lindsey is a cookie buyer.