4. My father hasn't smoked for two years

5. Why don't we use electricity economically

6. A whistle will be blown if there is an emergency 

7. They began to work in that factory ten years ago

8. He wishes he weren't late

9. The soil here is said to be very rich

10. Helen has been learnt Chinese since 2000

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4. My father hasn't smoked for two years 5.why don't we use electricity economically                                                   6a whistle will be blown if there is an emergency                                                     7 they began working in that factory two years ago.                                                      8he wishes he hadn't be late                         9 the soil here is said to be very rich.               10 Helen has been learned Chinese since200