QUES: acceptable
ANS: All native speakers have a grammatical competence which can generate an infinite set of grammatical sentences from a finite set of resources.

QUES: acceptable
ANS: Which attorney will give the closing argument hasn't been decided by them.

QUES: acceptable
ANS: Whom did Matt kiss?

QUES: unacceptable
ANS:
Who would you prefer for to win the race?