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CONTENT S 1

Lesson One 1

Lesson Two 13

Lesson Three 22

Lesson Four 32

Lesson Five 41

Review One 52

Lesson 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 180

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-Two 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．Sendirng 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 Most Useful Material 395

Ⅸ．Pollution 398

Reference Translations of Supplementary Reading 402

Appendixes 419