Chia động từ

Chia động từ
31. We stop once (buy) petrol and then we stopped again (ask) someone the way.
32. When I caught them cheating me, I stopped (buy) petrol there and started (deal) with your station instead
33. I tried (convince) him that I was perfectly capable of (manage) on my own, but he insisted on (help)
me.
34. Your hair needs (cut). You'd better (have) it (do) tomorrow.
35. I always try (come) in quietly but they always hear me (go) upstairs. It's impossible (climb) an old
wooden stair case at night without (make) noise. ......