The most valuable find of all was the ship's log book ,parts of which it was still possible to read

Question

这一句非限定从which指代read后的宾语the ship's log book, it形式主语，但是把it 去掉后变为parts of which was still possible to read .这里面parts of which 是主语 was 谓语动词，read 可以使不及物动词，这句话我觉得还成立，为什么不能把it 去掉呢
为什么改为parts of which could still be read是成立的呢？

Answer 1

看了这么多答案，上面的这个答案还是靠谱的。
parts of which it was still possible to read 这句想去掉it ，主语就变成了书了，也就是parts of which，后面必须是被动语态，to be read。
这句真正的主语是it，指代的是 to read 这件事，read这个动作肯定是人发出的所以用主动形式。
parts of which是一个倒装，完整语序是 it was still possible to read parts of which。理论上which应该换成it，但是首先一个句子出现两个it，不符合表达习惯。再一个it was still possible to read parts of which 这个句子没有连接词，前面是逗号，所以换成which 倒装之后来引导这个句子，并且还起到强调的作用。这应该是英语的一种表达习惯

Answer 2

在这个句子中“ parts of which”中的which是代词，而不是限定词。这里的which用来指代前面的“ship’s log book”。“ parts of which”之后“it was still possible to read”则是同位语从句（同位语从句的标志是句子结构完整），是“ parts of which”的同位语。

Answer 3

定从parts of which could still be read是一个parts of which 作主语的被动句
read-read-read，read的过分任然是read，LZ是不是这里迷糊了？