Hi Habib,
All three of these questions touch upon some core "PMI"-isms that should definitely be understood:
1) A project isn't done until the Closing processes are complete, i.e. just because the final deliverable has been accepted, doesn't mean your job as a project manager is done!
2) You can't inspect in quality, i.e. address quality concerns before inspection! (the earlier the better)
Knowing these two concepts will help you answer your questions.