Answer:
It looks like some parts of the conversation are missing, but here's what is provided:
Mylène: "Oui, il y a des élèves sympathiques... Et demain?"
Arnaud: "Peut-être, mais demain je retrouve aussi Dominique."
Mylène: "(5)________"
Arnaud: "Pas du tout!"
Based on this, it seems like Mylène said nothing in response to Arnaud's mention of seeing Dominique the next day, as indicated by the blank space with no text.