Svp aidez moi je ne comprend pas et je n'y arrive pas, c'est un devoir noter et je dois le rendre demain :(

1. Our art teacher has been ill for two weeks.
2. David has worked in an American lab since last Christmas.
3. My brother has had a new job for three months.
4. I have had a headache since this morning.
5. Jenny and Matt have been best friends since they went to university.
6. My parents have known the Mayor for five years.
7. She has ridden a horse very well since her eleventh birthday.