Please answer this: Question: "what is the second time period mentioned?" Context: "In 1931, RCA Victor introduced their vinyl-based Victrolac compound as a material for some unusual-format and special-purpose records. By the end of the 1930s vinyl's advantages of light weight, relative unbreakability and low surface noise had made it the material of choice for prerecorded radio programming and other critical applications. When it came to ordinary 78 rpm records, however, the much higher cost of the raw material, as well as its vulnerability to the heavy pickups and crudely mass-produced steel needles still commonly used in home record players, made its general substitution for shellac impractical at that time. During the Second World War, the United States Armed Forces produced thousands of 12-inch vinyl 78 rpm V-Discs for use by the troops overseas. After the war, the wider use of vinyl became more practical as new record players with relatively lightweight crystal pickups and precision-ground styli made of sapphire or an exotic osmium alloy proliferated. In late 1945, RCA Victor began offering special transparent red vinyl De Luxe pressings of some classical 78s, at a de luxe price. Later, Decca Records introduced vinyl Deccalite 78s, while other record companies came up with vinyl concoctions such as Metrolite, Merco Plastic and Sav-o-flex, but these were mainly used to produce "unbreakable" children's records and special thin vinyl DJ pressings for shipment to radio stations." Answer:
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Answer: end of the 1930s

Please answer this: Question: "What happened 3 years after the city elected Young?" Context: "In November 1973, the city elected Coleman Young as its first black mayor. After taking office, Young emphasized increasing racial diversity in the police department. Young also worked to improve Detroit's transportation system, but tension between Young and his suburban counterparts over regional matters was problematic throughout his mayoral term. In 1976, the federal government offered $600 million for building a regional rapid transit system, under a single regional authority. But the inability of Detroit and its suburban neighbors to solve conflicts over transit planning resulted in the region losing the majority of funding for rapid transit. Following the failure to reach an agreement over the larger system, the City moved forward with construction of the elevated downtown circulator portion of the system, which became known as the Detroit People Mover." Answer:
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Answer: the federal government offered $600 million for building a regional rapid transit system, under a single regional authority

Please answer this: Question: "How did the changes work?" Context: "In the United States, August Vollmer introduced other reforms, including education requirements for police officers. O.W. Wilson, a student of Vollmer, helped reduce corruption and introduce professionalism in Wichita, Kansas, and later in the Chicago Police Department. Strategies employed by O.W. Wilson included rotating officers from community to community to reduce their vulnerability to corruption, establishing of a non-partisan police board to help govern the police force, a strict merit system for promotions within the department, and an aggressive recruiting drive with higher police salaries to attract professionally qualified officers. During the professionalism era of policing, law enforcement agencies concentrated on dealing with felonies and other serious crime, rather than broader focus on crime prevention." Answer:
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Answer:
helped reduce corruption and introduce professionalism in Wichita, Kansas, and later in the Chicago Police Department