Some athletes have been accused of performing "blood doping" to improve their athletic performance. why would removing blood a month or so prior to performance, then reinfusing the blood shortly before a competition, boost performance? (mark all that apply)

This question appears to be incomplete. During blood doping, the athlete will have blood drawn and stored. The athlete will then allow sufficient time for the body to replenish the removed blood. Immediately prior to the event, the athlete will inject the stored blood back into his/her system. Blood doping effectively increases the number of red blood cells in the bloodstream to above normal. This enhances performance because  blood cells carry oxygen from the lungs to the muscles, and a higher concentration of oxygen in the blood can improve an athlete’s aerobic capacity and endurance.

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Mg is used to measure mass