Answer:
ATP is responsible for contraction and relaxation in muscles and plays a major role in the muscular system of our body.
The three observations that could help an individual in distinguising whether the organism is a fish or not is that it should live under water as fish can't survive without water, another thing is that it should laid eggs when it comes to giving birth because when it does not lay eggs but produces a living organism normally without an egg, it is considered to be a mammal and lastly, the appearance it possess such as having gils or fins.
HI there
I would go with D.cirrus
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