Complex sentence: At the beginning of the novel, Carrie has her first period while showering after a physical education class; she has no understanding of menstruation as her mother never told her about it, believing it to be sin.
Split into simpler sentences: At the beginning of the novel, Carrie has her first period while showering after a physical education class. She has no understanding of menstruation as her mother never told her about it, believing it to be sin.