it的指代问题

This passage and the broader portrayal of memory it helps to develop inthe novel demonstrates a prescient understanding on Woolf's part of our currentconception of how human memory works.

 

it代指的是什么啊，假如主语是This passage and the broader portrayal of memory 那样demonstrates 为何是第三人称单数？

这个句子应该有二个逗号：

This passage, and the broader portrayal of memoryit helps to develop in the novel, demonstrates a prescient understanding onWoolf's part of our current conception of how human memory works.

二个逗号之间为插入语，主语为单数名词 this passage. 所以谓语动词用单数形式。it 指代 this passage.