Simplify the following text for a Grade 11 native English-speaking person.
Original: After working for the KGB , Theremin worked at the Moscow Conservatory of Music for 10 years where he taught and built theremins , electronic cellos and some terpsitones ( another invention of Theremin ) .
Simplified: After working for the KGB , Theremin worked at the Moscow Conservatory of Music for 10 years where he taught and built Theremins , electronic cellos and some Terpsitones .