My father started to give up smoking last year

16..My father started to give up smoking last year.

=>My father has..............................................

17.They have worked in that factory since 2001.

=>They started.....................................................

18. Lan hasn't written to Maryam for a  month.

=>Lan didn't.........................................................

19. How long have you learnt French ?

=>How long ago.........................................?

20. How long have you bought this car ?

=>When did................................?