据宣称,一些早期文明中所创造出的技术只能从外星人那里学习了(钱伯斯)
It has been claimed that.这是一个主语从句,也就是说从句子的整体来说,that 后的成分都是整句话的主语,由于主语太长所以用it代替,it是一个形式主语,正常的语序应该是the technologies shown by some early civilizations could only have been learned from people from another planet has been claimed
再来分析主语这一句话the technologies shown by some early civilizations could only have been learned from people from another planet
这句话中the technologies shown by some early civilizations 是主语,could only have been learned 是谓语,而该句没有宾语,from people from another planet是这个句子的状语
再来看the technologies shown by some early civilizations ,这是一个词,technologies 是主干,shown by some early civilizations 是他的后置定语起修饰作用,
至于 could only have been learned,这是一个虚拟语气的用法,因为这个句子所陈述的事实是猜测,所以需要用虚拟语气,就是could+have/has done
我很认真的在讲解,你就采纳了吧