There is a new problem involved in the popularity of private cars ___ road conditions need ___.
A.that; to be improved
B.which; to be improved
C.where;improving
D.when;improving
请重点分析A和B选项,谢谢!

为什么不能选B呢?因为这里是that引导的同位语从句而不是定语从句。There is a new problem involved in the popularity of
private cars that road conditions need improving
(to be improved). 在这个句子中involved in the popularity of
private cars 是过去分词做定语修饰a new problem 。而that road
conditions need improving(to be improved).则是一个句子对a new problem的解释。而且在名词性从句中是不做成分的。