Problem: How does the sentence end?

Brian obtained a naturalization certificate before Michael because 
Answer: Brian had already been granted U.S. citizenship.

Problem: How does the sentence end?

John was texturing the drywall in the living room with a brush but the 
Answer: drywall was too hard.

Problem: How does the sentence end?

Christopher picked their nose in public, but Kenneth didn't. 
Answer: Christopher never cared what other people thought of them.

Problem: How does the sentence end?

Brian was fluent in French but Justin was a novice, so 
Answer:
Brian gave lessons in the language.