Answer:
The correct answer is a. ACTH
Step-by-step explanation:
Adernocorticotropic hormone(ACTH) is released by anterior pituitary in response to CRH hormone which is released by hypothalamus gland during stress condition. CRH hormone gives signal to anterior pituitary to release ACTH into the blood capillaries.
ACTH gives signal to adrenal cortex to release steroid hormones like cortisol which are essential in fight and flight response under any stress condition. So ACTH is necessary to initiate stress response of the body.