Answer: <em>C.) Cnidarians</em>
I'm not sure how exactly you wanted this question to be answered. You're either talking about the symmetry where animals would have two legs or two arms for example and thus producing a pair of each muscle on both sides of the body, or you're refering to the development of agonistic and antaonistic muscles where each of them served a different purpose; either extending or contracting.
Answer:
bio -characteristic of life
Answer: When your hypothalamus senses that you're too hot, it sends signals to your sweat glands to make you sweat and cool you off. When the hypothalamus senses that you're too cold, it sends signals to your muscles that make your shiver and create warmth. This is called maintaining homeostasis.