Poser la question correspondant à chacune des phrases suivantes en utilisant how long ou since when.
I've been working here since I arrived in London.
I've been living in Paris for five years.
He's been waiting at the door for an hour.
They've been practicing salsa since the beginning of the year.
I haven't seen them for years.
They've been fighting since they moved in together.
We've been discussing the matter for several hours.
I've been thinking about this since last year.
Fred has been unemployed since Fall.
This guy has been observing us for two hours.