What is ekg l, how does it works, and conditions it can aid in diagnosing. what are some of the limitations of this test?

EKG (electrocardiogram) -  A test that checks for problems with the electrical activity in the heart. It is done by placing electrodes on the skin and it records the results of the electricity in the chambers of the heart on a spike and dip tracing (the thing that draws the little line). It can aid in diagnosing heart attacks, angina (not enough blood flow to the heart muscles) , and pericarditis. Sometimes an EKG result will appear normal and not detect underlying problems and other times the results are non specific and can show in a variety of problems so the test can't say for sure what the problem is.  

Its either c or d. i would go with d though, because im not sure if its legal in all of the us