History 874 Social life and customs 190 Experiments 179 Handicraft 175 Science 172 Vocational guidance 168 English language 143 more ... Animals 140 African Americans 108 Presidents 93 Mathematics 89 Singers 83 Technique 78 Dinosaurs 75 Civilization 74 Social aspects 72 Nutrition 71 Sports 71 Children 69 Counting 69 Infancy 69 Authorship 65 Behavior 65 Readers (Elementary) 65 Civil rights 63 Consonants 63 Video games 62 Politics and government 59 Football 57 Race relations 57 less ...