Answer:
The answer is A: The nervous system uses electrical signals, while the endocrine system uses chemical messengers
Explanation: Your body uses electrical signals to move muscles and all types of things like that. The reason you can move your fingers on demand is because of your brain sending electrical signals. Now for pain your body uses chemical signals. Your brain sends out chemical signals letting you know that you are in pain in that specific area.
Two things human ancestors used sky for
What is the meaning of ancestor ?
An ancestor, also known as a forefather, fore-elder or a forebear, is a parent or the parent of an antecedent.
How do ancestors determine time ?
When two merkhets were aligned with the North Star, they formed a celestial meridian in the sky. The time could then be determined by counting how many stars crossed this line.
To learn more about ancestor here
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B. the vast array of digestive enzymes
C. Brunner's glands
D. the rugae