英语翻译I heard the main gate through which they had entered clo

I heard the main gate through which they had entered close with a resounding thud.
1求翻译,2问which 引导什么从句?
回答：
1）我听到大门“砰”的一声很响亮地关上了,而他们通过这道门已经进去了.
2）介词through+关系代词which引导一个限制性定语从句--through which they had entered,用来修饰限定其前的先行词gate,而close with a resounding thud 则是整个句子的谓语动词heard 的宾语补足语,其宾语是the main gate.
因为该定语从句译成汉语后太长,故将原句分成两部分.

我听到他们进去的那道大门随着响亮的重击声（哐当一声）关上了。这里which引导的是定语从句，因为entered through中的介词through 提前了，这个which不能用that来代替。

我听见他们走过/通过的大门砰的一声关上了。
Which引导定语从句是main gate的关系代词 本来是they had entered through the main gate，定语从句把through提前了。