Final answer:
The prepro-hormones of ADH and oxytocin are synthesized by the hypothalamus(A), not the posterior pituitary gland which only stores and releases them into the bloodstream.
Step-by-step explanation:
Prepro-hormones (of ADH and oxytocin) are synthesized by the (A)hypothalamus. The hypothalamus produces these hormones, which are then transported to the posterior pituitary gland. Although the posterior pituitary releases these hormones into the bloodstream, it does not synthesize them; it merely stores and secretes the hormones that were synthesized by the hypothalamus. Particularly, the paraventricular nuclei within the hypothalamus produce oxytocin, and the supraoptic nuclei produce the antidiuretic hormone (ADH), also known as vasopressin.