Simplify the following text for a Grade 9 native English-speaking person.
Original: The one-volume PropÃ dia is the first of three parts of the 15th edition of EncyclopÃ dia Britannica , the other two being the 12-volume MicropÃ dia and the 17-volume MacropÃ dia .
Simplified: The PropÃ dia is the first of three parts of the Encyclopaedia Britannica , , the other two being the 12-volume MicropÃ dia and the 17-volume MacropÃ dia .