Make you feel euphoria! its a "pleasure" chemical
Okay, warning: (COULD BE WRONG) Just to help you out I think 3, 5, and 6, are correct. (COULD BE WRONG, YOU MIGHT GET A LITTLE CREDIT)
Because the more someone exerts themselves the more oxygen and carbon dioxide out put ratio is greater. The more you run and the faster you run the more oxygen you loose which is supplied to your muscles including your lungs.
Oxygenated (arterial) blood is bright red, while dexoygenated (venous) blood is dark reddish-purple. The difference is color results from the electronic state of the iron ion (ferrous vs ferric), which in turn influences the π → π* and n → π* electronic transitions of porphyrin and hence its optical characteristics.
