英文语法问题

Question

In the nineteenth century, a novelist would bring his story to a conclusion by presenting his readers with a series of coincidences – most of them wildly improbable.
- most of them wildly improbable. 什么一个形式，起神马作用啊

Answer 1

这句话的意思是：在十九世纪，小说家会通过一系列的巧合呈现给读者，来结束他的故事，而这些巧合中的大部分几乎是不可能实现的。

--- most of them wildly improbable.中的them就是coincidences，所以破折号后面的短语只是补充说明coincidences，是补充说明的作用。