A:
1. Which flight did you take?
2. Which hotel did you stay at?
3. What music do you like?
4. Which magazine did you buy?
5. What company do you work for?
6. What language are you learning?
B:
1. What
2. Which
3. What
4. What
5. Which
C:
1. who
2. which
3. what
4. which
5. which
6. who