A simple machine is defined as:

A simple machine is defined as a tool that makes work easier with few or no moving parts. This definition highlights the fundamental purpose of simple machines: to reduce the amount of force needed to perform a task, enhancing efficiency. Simple machines, such as levers, pulleys, inclined planes, wedges, screws, and wheels and axles, allow individuals to exert a smaller force over a greater distance, therefore facilitating tasks like lifting, moving, or holding objects.

Contrasting this with the other options provides additional clarity. A complex device with numerous moving parts does not align with the essence of a simple machine, which is characterized by its simplicity and minimal components. Similarly, while some machines may require extensive energy input, this characteristic does not define a simple machine; in fact, one of their advantages is that they are designed to conserve energy and make tasks more manageable. Finally, a device that cannot assist in lifting does not fulfill the basic function of many simple machines, which often help lift or move objects as a core functionality. Therefore, option B accurately captures the essence of what a simple machine is.