Answer:
D. Response to external stimuli
Explanation:
The endocrine system is responsible for the production of hormones that regulate the most diverse physiological activities of the organism. It works together with the nervous system, in perfect sync that works as follows: nervous system receptors pick up external stimuli and from them induce the endocrine system to react.
For this reason, we can conclude that the main purpose of the endocrine system is to respond to external stimuli.
