Simplify the following text for a Grade 7 native English-speaking person.
Original: Since 1985 , the Britannica has had four parts : the MicropÃ dia , the MacropÃ dia , the PropÃ dia , and a two-volume index .
Simplified: Since 1985 , the Britannica has had four parts : the MicropÃ dia , the MacropÃ dia , the PropÃ dia , and a two-book index .