先看一个并列句：

I called him Tommy, and he soon began to answer to that name. 并列句。

that name 指前面的Tommy. 然后我们删去并列连词and, 用关系限定词which取代指示限定词that，并把to which name 前置于句首，就得到一个非限制性定语从句。which name 指代 Tommy：

I called him Tommy, to which name he soon began to answer. 主句+非限制性定语从句。