The correct option is A Hypothalamus
Diencephalon consists of thalamus and hypothalamus. Thalamus serves as relay station for sensory impulses as well as integration centre for recognition of pain, temperature and hard touch. The thermostat centre for temperature control is present in hypothalamus. Hypothalamus maintains the constant human body temperature by regulation of the diameter of blood vessels (constriction or dilation), shivering and sweating mechanisms.