Horroris a feeling of great shock, fear, and worry caused by something extremely unpleasant.
a feeling of 和后面的词是构成动宾关系吗？
caused by something extremely unpleasant.修饰什么？
Horroris a feeling of great shock, fear, and worry caused by something extremely unpleasant.
of表示同位关系。比如：Fear is a feeling. feeling在此为名词，不表示动作。cause 过去分词短语修饰 a feeling of great shock, fear, and worry 这个名词词组。
If you have afeelingof hunger, tiredness, or other physical sensation, you experience it.
of 仍表示同位关系。it指代feeling，等于such a feeling.