This paper consists of three sections, in the first section, the history of Rayleigh waves is introduced in detail and some problems unsolved are pointed out.

本论文包括三部分：第一部分详细介绍了瑞雷波的研究历史，并指出了存在的问题。

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The essence of human beings is an unsolved sphinx riddle haunting the thinkers and philosophers throughout the history of mankind.

人的本质问题是古今中外的思想家、哲学家求之不解的斯芬克斯之谜。

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It is an unsolved puzzle that adds even more intrigue to an already controversial figure in history, inspiring travellers to delve deeper into his life in both Europe and the Americas.

BBC: The mystery of Christopher Columbus��s legacy