Which Hanzi has a Regional Population of 4,591,972 in 2010?
CREATE TABLE "cities" (
  "city" text,
  "hanzi" text,
  "hanyu_pinyin" text,
  "regional_population_2010" text,
  "gdp_2011_billion_yuan" real
);
SELECT "hanzi" FROM "cities" WHERE "regional_population_2010"='4,591,972';