Throughout the day there are changes in carbon dioxide concentration. The peak is at 8 AM at 1000 ppm and The lowest is at 4 PM at approximately 700 ppm. The earlier it is, the more concentration of carbon dioxide and in the evening it is there is less concentration of carbon dioxide . Hope this helps :)
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Valves, they are like flaps of muscle that keeps the blood in its place util its ready to be pumped along.
A reason could be the bodies ability to process the water based vitamin as well as the person's diet. many things have b12 in it but choosing to cut something out, like meat, could cause a deficiency
