Which of the following depicts the usual order of extraction of teeth if serial  extraction is chosen as the treatment to alleviate severe crowding?
Primary canines are extracted to encourage alignment of the crowded incisors. However, the incisors align and upright, borrowing space otherwise needed for eruption of the permanent canine. Primary first molars are then extracted to encourage eruption of the first premolar so it may be extracted to make room for the permanent canine to erupt. These are followed by the permanent first premolar. 
Textbook of ORTHODONTICS Sridhar Premkumar
Primary second molars, primary first molars, permanent first premolars, primary canines
Primary canines, primary first molars, permanent first premolars
Primary first molars, primary second molars, primary canines
Primary canines, permanent canines, primary first molars, permanent first premolars