was to be fundamental to the development of life

答案：it was not obvious
解析："这一点不明显"中的"这一点"指的就是that后面的内容"水会对生命的发展起关键作用"，由此可知本句是由that引导的主语从句作真正主语，而前面使用it作形式主语．又根据前面的"在那时"可知，主句该使用一般过去时．综上，本题答案为：it was not obvious．

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