12. Chronically high levels of glucocorticoids can result in obesity, muscle weakness, and depression, a combination of symptoms called Cushing's syndrome. To determine which gland has abnormal activity in a particular patient, doctors use the drug dexamethasone, a synthetic glucocorticoid that blocks ACTH release. Based on the graph, identify which gland is affected in patient X, whose ACTH level in blood is effectively lowered by dexamethasone.
(A) Adrenal medulla(B) Adrenal cortex(C) Anterior pituitary(D) Posterior pituitary
(E) Thyroid gland