Final answer:
Decreased levels of serotonin are directly correlated with the presence of major depression, supporting the classic monoamine hypothesis. The correct option is B.
Step-by-step explanation:
Research suggests there is a direct correlation between the presence of major depression and decreased levels of serotonin (B). Major depression, affecting a significant portion of the adult population, is characterized by a range of symptoms such as persistent sadness, loss of interest in activities, and changes in appetite and sleep patterns.
While the precise causes of major depression are complex and multifactorial, involving genetic and environmental risk factors, a widely supported theory, the "classic monoamine hypothesis", posits that a decrease in neurotransmitters such as norepinephrine and serotonin contributes to the condition.
This is corroborated by the mode of action of various antidepressants that aim to increase the levels of these neurotransmitters.