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题目选项分析

比较两个句子语法结构语义，选出最佳答案：

To mine the ocean floor for gold may someday be worthwhile

, but at present, doing so is prohibitively expensive.

Mining the ocean floor for gold may someday be worthwhile

, but at present, doing so is prohibitively expensive.

写下分析过程，便于复习“吃透”这个句子：

答对用户笔记

题目基本信息

所属科目：语法SC
题目来源1：Ready4-0

难度：难