后置定语

和定语从句极为相似，区别就是引导词和B动词

就像汽车一样，有前置驱动，就有后置驱动。

which就是代表先行词，重复省略，are无意义，省略

【原创】这个which are 为什么可以被省略?
The gigure include a number of costs (which are) associated with air pollution.
【答】（1）你的句子应该改为： The gigure includes a number of costs (which are) associated with air pollution. 或者 The gigures include a number of costs (which are) associated with air pollution. （2）如果定语从句的谓语动词是被动语态，可以把主语（关系代词）和助动词 be 一起省略，用过去分词短语作后置定语。如：A substance (which is) made up of atoms of differrent kinds is called a compound. 由不同类型的原子构成的物质称为化合物。（摘自赵俊英：《现代英语语法》p.1307）在你的句子中， (which are) associated with air pollution 是定语从句，从句中的谓语动词 are associated 是被动语态，所以 which are 可以省略。