4 She began working as a secretary 6 years ago
_ S + began / stared + VIng/ to V : Bắt đầu làm gì
5 By the time Linda decided to hand in her essay, she had checked all spelling mistakes.
_ Thì quá khứ hoàn thành - by the time : S + had + PII
6 The last time I saw her was when she left for London
_ THe last time + Quá khứ đơn : Lần cuối ai đó làm gì