The correct option is B Dorsal segment of diencephalon
The diencephalon is the region of the vertebrate neural tube, that gives rise to posterior forebrain structures. The diencephalon is a part of the forebrain, that contains the thalamus, the hypothalamus and pituitary gland. The epithalamus is a (dorsal) posterior segment of the diencephalon. Three swellings develop in the lateral walls of the third ventricle, later becoming the epithalamus, thalamus and hypothalamus. The roof of diencephalon gives rise to the plexus choroideus and epiphysis. The downward extension of the diencephalon forms the infundibulum (future stalk and the pars nervosa of the hypophysis). Lateral evagination of diencephalon participates in the formation of the eye.