"Ding-dong!" Outside, the anxious group of high school seniors can hear the laughter and loud sound of their favorite music coming from inside the house. Erin runs to the door and opens it to see all her friends standing in front of the doorway. "Hey guys," Erin says as all of her friends come in, each giving her the usual kiss on the check and the mumbled, "Hi." They stop in the living room where the rest of their friends are. Some sit talking and some are on what they made a dance floor showing off their moves to the rest of the group. …