SELMER, Tenn. -- A tearful mother of two teenage girls killed when a speeding dragster skidded into a crowd demanded answers on Monday, saying the high-powered car should never have been on a city street."Somebody's got to take responsibility for this. I've got to bury my two girls," Darla Griswell said. "They were there just to have fun."Her daughters, Nicole, 19, and Raven, 15, were among six young people killed by the car when it fishtailed into the crowd Saturday at the Cars for Kids show in Selmer, a small town about 80 miles east of Memphis.At least 23 other...