Answer:
naturally living organisms
No they cant be mechanical because then something would have to generate their rays through the inventing of a machine.
Answer:
Stem cells provide new cells for the body as it grows, and replace specialised cells that are damaged or lost. They have two unique properties that enable them to do this: They can divide over and over again to produce new cells. As they divide, they can change into the other types of cell that make up the body.
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