The correct answer is B. unmindful.
The word “oblivious” means “not aware of or not paying attention to what is happening around you.” In this case, the person is so engrossed in the novel that they are not paying attention to their surroundings.
The word “precarious” means “dangerous or risky.” This does not make sense in the context of the sentence, as there is nothing dangerous or risky about being engrossed in a novel.
The word “aware” means “having knowledge or understanding of a situation.” This does not make sense in the context of the sentence, as the person is not aware of their surroundings.
The word “watchful” means “carefully observing or guarding something.” This does not make sense in the context of the sentence, as the person is not carefully observing or guarding their surroundings.