The image shows a circuit with a voltage source, resistors, and a box labeled M. M is likely a component whose identity we must determine from the options. Given the context, M is probably a capacitor, as it is placed in a circuit with DC source and resistors, and capacitors block DC once charged. The options show different symbols: the first is a capacitor, second is an inductor, third is a diode, and fourth is a battery. For DC circuits, a capacitor acts as an open circuit at steady state.

Final Answer: $M$ is a capacitor (first option).