Lack of regular exercise increases the risk of heart disease because:
A) the threshold of the sna node is increased, so the duration of the cardiac cycle is lengthened
B) Blood flows too slowly over time to provide adequate oxygento the myocardium
C) the valves lose tone, and don't close securely
D) pumping efficiency decreases because as stroke volume decreases, heart rate must increase to maintain cardiacoutput
E) respiratory rate is too low to take in sufficient oxygenfor optimal oxygenation of the blood.