练习材料：
Lesson30-1 Exploring the sea-floor
Our knowledge of the oceans a hundred years ago was confined to the two-dimensional shape of the sea surface and the hazards of navigation presented by the irregularities in depth of the shallow water close to the land. The open sea was deep and mysterious, and anyone who gave more than a passing thought to the bottom confines of the oceans probably assumed that the sea bad was flat. Sir James Clark Ross had obtained a sounding of over 2,400 fathoms in 1839, but it was not until of deep soundings was obtained in the Atlantic and the first samples were collected by dredging the bottom. Shortly after this the famous H. M. S. Challenger expedition established the study of the sea-floor as a subject worthy of the most qualified physicists and geologists.
应用配置：L0+L4
知识笔记：navigation/nævəˈgeɪʃən dredging/drɛʤɪŋ physicists/fɪzɪsɪsts
练习感悟：用时44分钟。生词不多，但是长句子挺多，需要注意停顿。
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