What issue led to the split between the Sunni and Shia Muslims?

Einar sees alexandra every day across the room in his history class but has never talked with her. einar likes the way alexandra looks, including the way she dresses and how she wears her hair. he's even more attracted to her apparent intelligence and the way she handles herself in class discussions and during interactions with the instructor. he'd like to know more about her, so he asks one of his friends about her. einar, using a passive strategy to gain information about her, is probably in the preinteraction awareness stage of any relationship that might develop between them. t/f