8. "Why didn't you mention the problem before?", I asked them (had).
→ I asked them why they had not mentioned the problem before.
9. You are unfit because you don't do enough exercise (would).
→ If you did enough exercise, you would not be unfit
10. I bought myself some good new clothes. I need them for my new job (which)
→ I bought myself some good new clothes which I need for my new job.