(After the Doctor saves Rose from the Auton attack in the basement, they travel in the lift)
Rose: Who are they, then? Students? Is this a student thing or what?
The Doctor: Why would they be students?
Rose: I don't know.
The Doctor: Well, you said it. Why students?
Rose: Cos… to get that many people dressed up and being silly, they've got to be students.
The Doctor: That makes sense. Well done.
The Doctor: They're not students.