CONTENTS 1
Lesson One 1
Lesson Two 13
Lesson Three 22
Lesson Four 32
Lesson Five 41
Review One 52
Lesspn Six 57
Lesson Seven 66
Lesson Eight 79
Lesson Nine 90
Lesson Ten 104
Review Two 119
Lesson Eleven 125
Lesson Twelve 137
Lesson Thirteen 152
Lesson Fourteen 165
Lesson Fifteen ………………………………………………？Review Three 196
Lesson Sixteen 201
Lesson Seventeen 215
Lesson Eighteen 231
Lesson Nineteen 246
Lesson Twenty 261
Review Four 276
Lesson Twenty-One 284
Lesson Twenty-Twe 300
Lesson Twenty-Three 317
Lesson Twenty-Four 336
Lesson Twenty-Five 354
Review Five 371
Ⅰ．The Story of Archimedes and the Bath 378
Supplementary Reading 378
Ⅱ．Sending Messages and Pictures by Satellites 379
Ⅲ．Living Under the Sea 381
Ⅳ．The World’s First Completely Automatic Railway 383
Ⅴ．Helicopters—Aeroplanes of Many Uses 386
Ⅵ．The Wonderful Talking Machine 388
Ⅶ．Taming the Sun 392
Ⅷ．Plastics—Man’s MostUseful Material 395
Ⅸ．Pollution 398
Reference Translations of Supplementary Reading 402
Appendixes 419