The correct answer is D: Current. The flow of electrons in an electric circuit is called current. Current is the movement of electric charge (electrons) through a conductor, measured in amperes. In a circuit, electrons flow from the negative terminal of a power source (like a battery) through the circuit to the positive terminal. This flow of electrons is what we call current. Current is one of the fundamental electrical quantities and is essential for understanding how circuits work. Without current flow, there's no electrical activity in a circuit - no power delivery, no signal transmission, nothing happens.