first one, nerve cells are used to send messages from different parts of the body to the brain.
Answer:
it's an example of a closed circuit
Answer:
Gas exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them. As shown below, inhaled oxygen moves from the alveoli to the blood in the capillaries, and carbon dioxide moves from the blood in the capillaries to the air in the alveoli.
Answer:
the answer is A) carbon
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