第17题: [单项选择]The author compare the ocean bottom to a "frontier" in paragraph 1 because it______. A. is a quite promising place. B. is out of the understanding of many scientists. C. attracts courageous explorers. D. is an unknown research area to the scientists. 参考答案:D 答案解析:[精解] 本题是一个推断题,即给出一个单词,要求考生理解该词在上下文中的意思和作用。解答这种推断题要建立在对段落乃至全文的主题有—个总领的看法上,分析具体句子:“The ocean bottoma r