Is this the reason at the meeting for his carelessness in his work>

问题描述:

Is this the reason at the meeting for his carelessness in his work>
请问括号中的是什么从句?定语还是同位语,为什么?

是定语从句
(he explained)
为从句,从句里缺少宾语,所以为定从
我们说定语从句,关系代词代替先行词在从句里作主语,宾语或表语
而同位语中的关系词在从句里不做成分,且that不可省略