Réponse:

1) You know, I think you should take a holiday. (demande/conseil poli, donc should)

2) Tell Mark he must tidy his room at once (il doit absolument ranger sa chambre, ordre donc must)

3) Visitors are reminded that they must keep their bags with them.

4) I'm sorry, but you should go. We don't want you here.

5) I really should go on a diet. I'll start today !

6) I suppose I should write to Aunt Rachel one of these days.

7) You absolutely must check the tyres before you take the car out today.

8) All officers must report to the Commanding Officers by midday.

9) You should have your hair cut at least once a week.

10) I think everybody should know two or more languages.