有关形容词比较级修饰名词

有关形容词比较级修饰名词：

Hydrogen, which is ______ than oil, is pretty easy to produce...

答案是d.a much more abundant energy source, 但我的问题是选项b中 an energy source more abundant 为何不对，形容词比较级做后置定语修饰名词不是等于省略的定语从句吗？.. is an enrgy source which is more abundant than oil

选A，是hydrogen和oil作比较。选B 成了energy source和oil作比较了，不符合逻辑。