What test involves placing sensors on the body to monitor heart's electrical activity?

The correct choice is the Electrocardiogram (ECG) because this test specifically involves attaching electrodes to the skin to capture and record the electrical activity of the heart. The ECG provides valuable information regarding the heart's rhythm, the size and position of the heart chambers, and any potential damage to the heart muscle.

Electroencephalogram (EEG) focuses on recording electrical activity in the brain and does not assess heart activity, making it irrelevant to the question. Echocardiography uses ultrasound waves to create images of the heart's structure and function, but it does not measure electrical activity directly. An Electrophysiological study (EPS) is a specialized procedure involving catheter insertion into the heart to map electrical impulses and diagnose arrhythmias, but it is not a test conducted through surface electrodes like the ECG. Hence, the ECG is the appropriate answer as it directly monitors the electrical activity of the heart using non-invasive sensors placed on the body.