Simplify the following text for a Grade 10 native English-speaking person.
Original: The Russian ballet patriarch Fyodor Lopukhov has called Swan Lake a `` national ballet '' because of its swans , who originate from Russian lyrically romantic sources , while many of the movements of the corps de ballet originated from Slavonic ring-dances .
Simplified: Fyodor Lopuokhov called Swan Lake a `` national ballet '' because the swans come from Russian sources , while many of the movements of the corps de ballet came from Slavonic ring-dances .