Simplify the following text for a Grade 10 native English-speaking person.
Original: For instance , the conversations between Octavian and the Marschallin in the first act use the familiar `` you '' but switch back and forth between more formal speech ( Sie ) and the familiar `` du '' .
Simplified: For example : Octavian and the Marschallin often use the familiar `` you '' but sometimes use ( Sie ) when they are being more formal .