Lesson15-The riddle of time I. Text Analysis Structure Part 1(Paras. 1-2): A discussion of the definition of time Part 2(Paras. 3-14): The historical development of human beings timekeeping Part 3( Paras. 15-19): The body clock of human eings Part 4( Paras. 20-22): Conclusion W B TL E The end of structureLesson15—The Riddle of Time W B T L E Part 1 (Paras. ): Part 2 (Paras. ): Part 3 (Paras. ): Part 4 (Paras. ): I. Text Analysis Structure 3—14 15—19 A discussion of the definition of time The historical development of human beings’ timekeeping The body clock of human beings The end of Structure. Conclusion 1—2 20—22