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

Answer: Option B

precarious : not securely held or in position; dangerously likely to fall or collapse.
unmindful : not conscious or aware.
aware : having knowledge or perception of a situation or fact.
watchful : watching someone or something closely; alert and vig
oblivious : not aware of or concerned about what is happening around one.


Synonym of oblivious is unmindful