Why my answer "you study in the classroom" , was not accepted ? In my humble opinion, "classroom" is both a honest English word and,it is offered by DL itself, as a correct translation for the Spanish word "clase", in this context !
However, a few "common" Spanish nouns always take the definite article, even though we don't translate the definite article into English. Those nouns generally refer to places.
These nouns include: Prision, clase, comida (not a place), , hospital, escuela, cama, casa, iglesia, trabajo, Cárcel, colegio,
They really should pay more attention to the way things are worded in these courses. They keep treating the present indicative tu form of the verb as if it is present progressive but then they suddenly expect you not to without any reason at all. Are they even looking at the reports or not? they should get more team members for Spanish.