Fight-or-flight reactions cause activation of.

The correct option is C The adrenal medulla, leading to increased secretion of epinephrine and norepinephrine
The inner portion of the adrenal gland, known as the medulla, secretes epinephrine and norepinephrine, the hormones important in the fight or flight reaction to a threat or sudden stress. The medulla is known as emergency gland develops from nervous tissue; the autonomic nervous system controls its secretions. The secretion of these hormones is stimulated when nerve impulse reach the adrenal medulla through sympathetic nerve fibres. These hormones act on organs and tissue supplied by sympathetic fibres and produce effect like those of sympathetic stimulation. Noradrenaline is also released at sympathetic nerve terminals to transmit nerve impulses from them to smooth muscles and glands.

So, the correct answer is option C.