No matter how you slice it the answer is C.
@Karien
I've no idea what the raws say, but the comic definitely shows praxis not practice; during the class, at least.
The instructor performs the exercise as a demonstration (praxis) in class. The students are only shown repeating the exercise...
@Kirin-kun
@Hadski
I think people are talking about it openly because it, or at least part of the details of it, has already come up in the manga; but, uh, I can't recall whether that happened too clearly either so maybe I'm remembering that wrong.
@Syapaaye
Rokuko starts calling her Haku instead of No.89 once Kehma mentions that 89 is read as Haku in his language, which is probably what you're remembering.
Lyon Raverio picked the name because it means 'white' in whatever language they're speaking.