The *heart* is the main organ of the circulatory system.
The circulatory system consists of three independent systems that work together: the heart (cardiovascular), lungs (pulmonary), and arteries, veins, coronary and portal vessels (systemic). The system is responsible for the flow of blood, nutrients, oxygen and other gases, and as well as hormones to and from cells.
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The answer is
<span>B.They help produce plasma cells.
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Answer:
It probably said one of two things:
1) "I'm not half the cell I used to be."
2) "I'm seeing double."
At the top of the body of a water, there is a lot of light from the sun, which also means a lot of solar energy. This allows for a fruitful photosynthesis.
In contrast, at the bottom of the water, there isn't as much, or sometimes any, sun light. Because of this the organisms at the bottom of the body of water
<span>D. must rely on other means than photosynthesis
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