Language points

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1.Perhaps it is the desire for solitude or the chance of making an unexpected discovery that lures people down to the depths of the earth.

背诵句型

结构分析: it is the desir e ......or the chance ......that......，运用了强调了句式，被强调的部分是句子的主语:it is the desire ......or the chance

eg: It is the desir for knowledge that lures her into the book world. 是她对知识的渴求吸引她走进书的海洋。

2.It can take as long as eight days to rig up rope ladders and establish supply bases before a descent can be made into a very deep cave.

结构分析:  before 引导时间状语从句。It 为形式主语，as long as eight days 作谓语can take 的宾语，不定式短语to ring up rope ladders and to establish supply bases作真正的主语。

词汇注释：

ring up 草草作成         eg. Soldiers rigged up tents for the night.

make a descent 下落新概念英语青少版