not one of them is/are?

问题描述:

not one of them is/are?
one of them is...这我知道
但我好像又看到not one of them用的是are...
not one of them 到底用is还是are呢?
哦,貌似问错了
找到原题了
Not one of the doctors who ( ) treating my sister knows exactly what is wrong with her.
由此可知 not one至少是knows。
那么这个who的定语从句到底跟的的是doctors还是not one呢?
如果把题目改成
One of the...
又应该如何呢?

这样说的话,应该用are
用is还是are,取决于合成主语后,其含义为单数还是复数,复数,就用are