高中英语语法，定语从句求解？the river __ banks... 为什么用whose 不用of which??

Question

14。the river __ banks used to be covered by the fruit trees and flowers is now seriously pollutered
A of which
B along which
C where
D whose

参考答案D
谁解释一下A选项。

Answer 1

首先of which应该适用于非限制性定语从句，又都好的那种，其次就算是非限制性的定语从句也应该是of which the banks 或the banks of which 两个要变成四个本回答被网友采纳

Answer 2

句子的主干是the river is polluted 。关系代词前的介词跟后面的动词有关，把of移到polluted后面，则成了the river which banks 。。。先行词发生变化这就错了，river的两岸曾经树木覆盖，只能用whose。

Answer 3

空后紧跟banks，再后有是used to be,说明要么banks是主语，则空要么是修饰banks 要么是地点之类的状语。
of which=of the river 后要再加banks就翻译不通啦