Whose discovery of radium changed the world's view of the atom

From 1990 to 2008, by what percent did the world’s most developed economies cut their greenhouse gas emissions?

Jacksonian democracy promoted new methods of political campaigning. one such technique was mudslinging. what was its effect on the presidential candidates?

Which source would best a historian understand the effect of the great chicago fire on families? a. a biography of a chicago family displaced by the fire b. a letter from a grandmother in new york to her family in chicago c. a newspaper editorial about families who were displaced d. an oral history dictated by an adolescent who fled the fire