Problem: How does the sentence end?

Elena had a much better speech than Kayla had because 
Answer: Kayla stuttered during the speech.

Problem: How does the sentence end?

Natalie hated cats while Lauradidn't so 
Answer: Natalie got upset when the other brought one home.

Problem: How does the sentence end?

Matthew played all the trendy mobile app games but not Donald because 
Answer: Donald had a house phone.

Problem: How does the sentence end?

Nelson cares passionately about the environment, while Kevin does not care about sustainability. 
Answer:
Kevin never disposes of recyclables properly.