I.Choose the best answer:(4) 16. I ____ how to dance when I ____ six years old. A. don’t know / was B. didn’t know / am C. didn’t know / was D. haven’t known/was 17. Nam is a careful driver but yesterday he ____ carelessly. A. drove B. had driven C. drives D. was driving 18. Do you like swimming, Ba? – I ____ when I was a child but not now. A. do B. did C. have done D. had done 19. I ____ her at the school gate yesterday. A. met B. meet C. had met D. am meeting 20. She ____ English when she was six years old. A. learned B. has learned C. is learning D. had learned