Problem: How does the sentence end?

Samuel failed their final exams while Brian passed them, so 
Answer: Brian had no need to retake their classes in summer school.

Problem: How does the sentence end?

It was easy for Felicia but not Laura to win the race because 
Answer: Felicia ran very quickly.

Problem: How does the sentence end?

The teacher asked Ian but not Robert if they were going to organize their notebook because 
Answer: Ian was disorganized.

Problem: How does the sentence end?

Laura thrives on conflict while Christine avoids it, so 
Answer:
Christine usually backs down from a fight.