der Lehrer des Lehrers
with the translation underneath: the teacher of the teachers
but shouldn't that be "of the teacher", i.e. singular?
The "s" on the end of some nouns in the genitive is a little trap for English speakers !
This is repeated in the "Know it" test, and I think in the other reinforcement tests as well.
I think (please correct me if I'm wrong) that "of the teachers" would be "der Lehrern" or "der Lehreren".