[Q]: How does the sentence end?

The man could write instructions for building engines but not houses, since 
OPTIONS:
- engines were his area of expertise.
- houses were his area of expertise.

[A]: engines were his area of expertise.
QUES: Continue writing.

The man wore a vest to the wedding but not to the birthday party since the 

OPTIONS:
- party was casual.
- wedding was casual.
+++++++++
ANS: party was casual.
Problem: How does the sentence end?

Jennifer suffered from diabetes but Samantha did not. 
OPTIONS:
- Jennifer had to inject themselves with medicine every week.
- Samantha had to inject themselves with medicine every week.
Answer: Jennifer had to inject themselves with medicine every week.
sentence: The speech was louder in the auditorium than the park because there were more speakers at the  OPTIONS:
- auditorium .
- park .
complete: auditorium .
Mary wanted to change her shoes because they felt too tight on her feet.  The 
OPTIONS:
- feet were too small.
- shoes were too small.
shoes were too small.
Problem: Continue the following story.

Because Brett was being helped with moving by Donald, 
OPTIONS:
- Brett was feeling very appreciative when the help was offered.
- Donald was feeling very appreciative when the help was offered.
Here's how I want to continue it:
Brett was feeling very appreciative when the help was offered.