The novel was so interesting that I was oblivious of my surroundings.

Answer: Option D

Indifferent : having no particular interest or sympathy; unconcerned.
Watchful : watching someone or something closely; alert and vigilant.
Aware : having knowledge or perception of a situation or fact.
Unmindful : not conscious or aware.
Oblivious : not aware of or concerned about what is happening around one.

Synonym of Oblivious is Unmindful