Answer: a. Coordination
Step-by-step explanation:
What we see here is the Endocrine system in action. When in action it works by releasing chemicals into the bloodstream known as hormones which then travel to the tissues or organs involved and upon reaching there effect change.
For example, when Adrenaline is released by the Adrenal gland, it travels through the blood to the Heart where it increases the heart rate.
This system usually goes into action in reaction to changes in the body that threaten homeostasis therefore it's purpose is to COORDINATE and control the body to ensure that a stable environment is maintained.
Your question was unclear so I attached the question here to help.