The correct answer is A. reverie.
A reverie is a state of deep thought or abstraction, often accompanied by a pleasant feeling of well-being. It is similar to a daydream, but it is typically more focused and less fanciful. People often enter a reverie when they are alone and relaxed, and they may find themselves lost in thought for minutes or even hours.
The other options are incorrect because they do not accurately describe the state of being in a brown study. Fear is a feeling of anxiety or dread, sleep is a state of unconsciousness, and a dream is a series of images, thoughts, and sensations that occur involuntarily in the mind during certain stages of sleep.
In the context of the question, the woman is clearly not afraid, asleep, or dreaming. She is simply lost in thought, and she is so focused on her reverie that she does not even notice the speaker’s entrance.