应该是宾语从句。
decide which... decide 是及物动词 ,后面跟上的是宾语,which 引导一个主谓结构,它是宾语从句。
详解:我把你给的介词扩展成一个复合句让你理解为什么它是宾语从句。
You should think it over before you decide which car you want to buy. 在你决定你要买哪一部车前,你应该仔细思考这件事。
上面的句子是含有两个从句的复合句。主句是You should think it ove
before you decide which car you want to buy 它是时间状语从句
which car you want to buy 宾语从句
在before 的状语从句中,谓语动词decide 后面出现了宾语从句。
你给出的问题是放在before deciding which
至于为什么动词decide变成了动名词deciding,那是因为decide 放在介词before后面了,根据语法规则,介词后面的动词都要用动名词doing而不能用动词原性,因为它是介词+宾语结构,动词只能作谓语。
before doing sth. 介词短语作时间状语 (用于简单句)
=before sb. does sth. 时间状语从句(用于复合句)
下面我把上面我写的复合句变为简单句:
You should think it over before deciding which car you want to buy. 在你决定你要买哪一部车前,你应该仔细思考这件事。
before you decide which 用于 复合句
before deciding which 用于简单句
before deciding which (which 引导宾语从句)