20 pack contains the following titles:
Level 21 = Free Trade; GM Foods; Rainforests; The Story of Icarus.
Level 22 = Antibiotics and Vaccines; Drilling for Oil; Germs; Run For Your Life.
Level 23 = Cell Science; Gladiators; The Ideas and Beliefs of Ancient Greece; Noah's Secret.
Level 24 = Race to the South Pole, Research in Antarctica; Space Tourism; The Great Pharaoh's Secret Box.
Level 25 = Nuclear Energy; Skyscrapers; The Channel Tunnel; Out of this World