Which of the following aspects of bipolar disorder predicts a favorable response to lithium treatment?

Choice A reason: Rapid cycling is associated with a poorer response to lithium, often requiring alternative or adjunctive therapies. Choice B reason: Clear euthymic intervals between episodes are associated with classic bipolar disorder, which predicts a favorable response to lithium treatment. Choice C reason: Psychotic symptoms do not reliably predict lithium response; these patients may require additional antipsychotic therapy. Choice D reason: Mixed episodes often respond less predictably to lithium alone and may need combination therapy.