请问这个个句子中Which代表什么?

题目

请问这个个句子中Which代表什么?
They added that China's move also helped soothe concerns about the speed with which its economy was slowing.
这个句子中that之后的句子应该是add的宾语从句,但这个从句是“that China's move also helped soothe concerns about the speed with which its economy was slowing”整个后半部分么?还有就是which在这里面代表什么结构?which是定语从句的先行词么?
如果是定语从句的先行词的话,那定语从句是哪一个?

答案

They （主句主语）
added（主句谓语）
that（宾语从句连接词,或先行词）
China's move（宾语从句里的主语）
helped（宾语从句里的谓语）
soothe concerns（动宾结构做 helped 的补语）
about the speed（介词短语作定语修饰 concerns）
with which（引导定语从句修饰 speed,which 代 speed）
with 的用法看倒过来的句型就容易理Its economy was slow down with the speed.