Unit 01 Pen Pals from a Bottle Unit 02 America's National Flower Unit 03 The World's Icebox Unit 04 Cartooning's Serious Side Unit 05 The Day Niagara Stopped Roaring Unit 06 The Day the Babe Called His Shot Unit 07 A Seal Name Andre Unit 08 Are Airlines Just for People? Unit 09 Who Invented the Potato Chip? Unit 10 An American Revolution Heroine Unit 11 A Simple Life Unit 12 High Sierra Hero Unit 13 Hunt for Black Gold Unit 14 Power and Poetry on Ice Unit 15 Manx Means Doubles Mystery Unit 16 Steps in Time Unit 17 Astronomers Tune In on Space Unit 18 Daredevil of Yesteryear Unit 19 Mystery Writing Unit 20 Superstition and Science