Unit 1 Pesos in the Sea

Unit 2 Early Days of the Mail

Unit 3 The Vanished City

Unit 4 Man Hunters of the U.S.A

Unit 5 Emergency Jump

Unit 6 The Gift of Fire

Unit 8 What Makes the Weather

Unit 9 Icarus

Unit 10 The Cowboy's Bandanna

Unit 11 Why Study Math?

Unit 12 California's Gianst

Unit 13 The Big Wind

Unit 14 A Pound of Butter

Unit 15 Beauty on the Witng

Unit 16 Death of a Gull

Unit 17 Postmen with Feathers

Unit 18 The Beau Cather

Unit 19 How Stanley Found Livingstone

Unit 7 Disaster in Dayton

Unit 20.Traveling in the Jungle

Unit 21.He Led a Useful Life

Unit 22 Rain Is Born.

Unit 23 Elas Kills a Buffalo

Unit 24 A Roof over Our Heads

Unit 25 Rubber

Unit 26 The History of Books

Unit 27 Horace Greeley

Unit 28 Looking Nice

Unit 29 Animal Education

Unit 30.Arctic Adventure

Answer Key(另附)