You would use vous, since M. Bernard means Mr. Bernard, and is formal. Generally if you're addressing someone as "Mme." "M." or "Mlle.", it's formal.
Bonjour !
Answer:
5) Veulent-ils dîner avec nous ?
Do they want dinner with us?
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Nous mangeons un sandwich en ville.
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I think that it's A. Hopefully I'm correct. Please tell me if I'm wrong
