Starting in the mid-1990s, major American cities began a radical transformation. Years of high violent crime rates, thefts, robberies, and inner-city decay suddenly started to turn around. Crime rates didnt just hold steadily, and they began falling faster than【M1】______ they went up. That trend appeared in practically every【M2】______ post-industrial American city, simultaneously. 'The drop of crime in the 1990s effected all geographic areas【M3】______ and demographic groups,' Steven D. Levitt wrote in his landmark paper on the subject, Understanding Why Crime Fell in the 1990s, and elucidated further in a best-selling book Freakonomics. 'It【M4】______ was unanticipated that it was widely dismissed as temporary or【M5】______ illusory long after it had begun.' He went on to tie the drop to the legalization of abortion 20 years much earlier, dismissing police【M6】______ tactics as a cause but they failed to explain the universality and【M7】______ unexpectedness of the change. Alfred Blumsteins The Crime Drop in America pinned the cause of crime solely on the crack epidemic but gave the credit for its appearance to those self-same【M8】______ policing strategies. Plenty of other theories have been offered to account for the double-digit decrease in violence, from the advent of 'broken windows' policies, three strikes laws, changing demographics, gun control laws, and the increasing prevalence of cellphones or an【M9】______ upturn in the economy and cultural shifts in American society. Some of these theories have disproven outright while others【M10】______ require a healthy dose of assumption to turn correlation into causation. 【M1】