What does the term "sullen" primarily mean?

The term "sullen" primarily refers to a mood characterized by gloominess or a sulky demeanor. When someone is described as sullen, it often means they are silent or brooding because of their sadness or displeasure, leading to an atmosphere that feels heavy or withdrawn. The correct choice encapsulates this idea of being sad or sulky perfectly.

In contrast to the correct answer, the other options convey very different emotions. Joyful and cheerful indicate a positive, upbeat attitude, which directly opposes the meaning of sullen. Excited and enthusiastic also reflect a lively, exuberant state that is not at all aligned with the gloominess associated with sullen. Lastly, indifferent and apathetic suggest a lack of interest or concern, which doesn't capture the emotional weight of sadness that "sullen" implies. Therefore, choice B is the most fitting definition of the term.