＜＜求助贴＞＞ 关于manhattan上的一个语法点，求大牛指导

泡泡93

  在manhattan 5th chapter 4 parallelism这一章中说，the subordinators do not have to be identical,然后举了一个例子：
There are many people who speak English But whose parents do not.
    但是在chapter11补充章节 中又说，only clauses starting with the same word should be made parallel. In general,clauses should not be made parallel to anything besides another clause.
i.g.:A mastodon carcass, which has been thawed only once and which is still fresh, is on display.
       所以问题就是在平行结构中从句先行词到底需不需要一样呢？

        希望大神解答！