The Chemical Imbalance Description of Depression and the Link to Serotonin

The chemical imbalance description of depression and the link to serotonin levels in the brain is controversial because

A) it is an oversimplification of the relationship between neurotransmitters and mood
B) serotonin is not involved in the brain's control of mood
C) studies show that delivering dopamine to depressed patients is as effective as delivering serotonin
D) it is a false statement proposed by pharmaceutical companies