1. Only then did we decide to answer violence with violence.
2. I felt bad the first time I talked to the group. the first time相当于连词，用来引导从句
3. He taught us during the lunch breaks and the evenings when we should have been asleep. should have done 本应做而未做
needn’t have done 本不应做而做了 can’t have done 过去不可能做过
4. The time when I first met Nelson Mandela was a very difficult period of my life
5. Mandela was the black lawyer to whom I went for advice.
6. He was generous with his time, for which I was grateful.
7. The school where I studied for only two years was three kilometers away.