In order to ensure sequential contractions of the heart chambers, jorge had a mechanical pacemaker inserted. what part of jorge's heart did this mechanism replace

Ithink it would be a and b

Smoking damages the respiratory system by inhalation of a foreign substance, that is absorbed and residue is left behind on our lungs sponge like substance. the gas that is inhaled also increase your blood pressure and dilates your blood vessels. also the process of inhaling and exhaling the smoke it causes irritation to the throat and mouth. smoking can cause lung cancer and other respiratory and circulatory diseases. 

Target heart rate is the answer