Ответ:
1. I am working at this problem
2. I was working at this problem
3. I will be working at this problem
4. John and Jane have not learnt this poem properly
5. John and Jane had not learnt this poem properly
6. John and Jane will not have learnt this poem properly
7. Does this old professor come to the university at 2?
8.Did this old professor come to the university at 2?
9. Will this old professor come to the university at 2?
Объяснение: