"Corinna and Stephanus have a teacher."
Translation:Corinna et Stephanus magistrum habent.
I just used "magistram," but it accepted it as a typo rather than simply a correct answer. It's showing the correct answer as "magistra" (which is not in the accusative case, so is incorrect). Not sure how to report this, though, since mine wasn't marked incorrect and I can't report their sentence as incorrect.