The correct answer is D. unmindful.
The word “oblivious” means “not aware or unconscious of something.” In the context of the sentence, the speaker is so engrossed in the novel that they are not aware of their surroundings. This is consistent with the definition of “unmindful,” which means “not paying attention to or considering
something.”The other options are incorrect because they do not accurately describe the speaker’s state of mind. The speaker is not indifferent to their surroundings, as they are clearly interested in the novel. The speaker is not watchful, as they are not paying attention to what is going on around them. The speaker is not aware, as they are not conscious of their surroundings.
In conclusion, the correct answer is D. unmindful.