"το τρένο είναι γρήγορο όχημα" is marked as incorrect but unless I'm mistaken, the indefinite isn't really needed
Just added, thank you! ^.^ (And Sean's indefinite article crusade continues. :P)
And continue it shall until they are all expunged ;-)
Προσθέστε και το τρένο.
Προστέθηκε ;)