The surrounds the third ventricle and its two most important structures are the

Covered by the two cerebral hemispheres, the diencephalon is the structure of the central nervous system that surrounds the third ventricle. It is composed of several other structures. The most important of them are the Thalamus, which plays a very important role in movements and emotions; and the Hypothalamus, which provides functions including thermoregulation, appetite and regulation of the sleep-wake cycle.

answer; i believe that the correct answer is(d) nondisjunction during meiosis;

thinking it would be physical characteristics