I think the answer is D, hope this helps you and have a great day!!!! :)
Answer:Smooth muscle is called involuntary muscle because you can not control this type of muscle movement. These muscles line internal organs, blood vessels, and organs such found in the digestive and reproductive systems.
Explanation:
The digestive system breaks down (catabolizes) food into its nutrient parts. The circulatory system brings those nutrients to the cells where they are needed. One of the main requirements of the cells is for energy, which the body manufactures by combing nutrients (especially carbohydrates, glucose, glycogen, and glycogon) with oxygen. The body takes in oxygen via the respiratory system and distributes it via the circulatory system.
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If you round it up you will get 20.