Clay,which was just below the surface of soil in certain clay-rich areas has to be dug up by a digger.对于这个句子后半部分的has to
问题描述：
Clay,which was just below the surface of soil in certain clay-rich areas has to be dug up by a digger.对于这个句子后半部分的has to be的结构不明白,为什么可以这样用语法结构? 它的意思是主语也是clay,但这样直接在上个句子前加has to be dug up无法理解其逻辑
答
被动句.be 过去分词.被挖.which was•••areas 这个句子不是完整了吗后面再加个has to be这样的语法结构是什么？Clay,[which was just below the surface of soil in certain clay-rich areas] has to be dug up by a digger.括起来的是状语从句就是比如说＂教英语的老师喜欢他＂教、喜欢也是两个动词实际上是老师喜欢他、又补充了老师是教英语的。道理一样的非常感谢，我再好好琢磨着！不会再问〜〜