题目内容
2. As we all know,great scientific achievements are the results of years of trying to create something before (exist)
正如我们所知道的,伟大的科学成就缘于多年努力去创造某些以前不存在的东西。
2. that has never existed定语从句中的谓语动词的单复数须与that所修饰的名词或代词一致。此句先行词是something
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