Which sentence below has correct subject/verb agreement?

A. She said her friend and former room-mate were going to be the maid of honor at the wedding.

B. We learned that the winner and still champion are going to compete in the race.

C. The chief and foremost expert in the field is speaking in the assembly today.

I would go with the last sentence.

The question is whether those phrases are speaking of the same person:

A. her friend and former room-mate

- this is the same person, if it was two people, it'd be "and her"

B. the winner and still champion

-again, the same person, requires singular verb

C. The chief and foremost expert

-again, the same person: requires a singular verb and actually has a singular verb, correct answer!