Which training principle states that exercising a certain body part or practicing a particular skill primarily develops that part or skill?

The training principle of Specificity states that exercising a certain body part or practicing a particular skill primary develops that part or skill. Ensuring that exercise programs have specific goals would make training a lot easier and improvements more noticeable. 

If you want to be a good runner, you have to incorporate running into your training program. If you want to beat that time in swimming, you have to incorporate sprints in your swim training. You are not only training your muscles for the activity, you also need your brain to be trained enough for the exact activity or skill that you are going to perform. Specificity principle reminds and ensures an individual to assign activities that would help meet specific goals.

the last statement is correct i.e.

the artificial heart has limited usefulness but can prolong life or be a tool to use while waiting for a transplant.

when your heart is not pumping enough blood around your body because your heart is severely failing, you may need an artificial heart. an artificial heart is a mechanical device, about the size of an orange, that is connected to your heart or implanted in your chest to or replace a failing heart.

20 times a minute is usually the average respritory rate of an adult. additionally the patient is breathing on his own, is clearly maintaining his airway, and is intaking a sufficient amount of air. you shouldn't use a bag valve mask, cpap, or other form of positive pressure ventilation, unless the patient has lost control of his airway, and is not breathing (apneic) or has rapid breathing or slow and shallow respirations. this patient would most likely and should be put on an non-rebreather mask or nrb attached to 100% high flow oxygen at 15 l/min. don't use a nasal cannula, as the amount of oxygen it provides is limited with a rate of 6 l/min.