Refer to figure.
Piston Engines can have their power increased in three main ways, by increasing the size of the engine (displacement), increasing the RPM, or increasing the pressure of the air/fuel mixture (called the Manifold Absolute Pressure, MAP). This last case is why we might use a turbocharger in our car engines, so we can have a small, efficient engine, with extra power available from a turbocharger (which compresses the intake air) when needed. "Supercharger" is the basic term for a device that compresses the intake air, and turbochargers are specific types of superchargers, which perform this task by using the extra energy left in the exhaust gasses (very efficient).

Engines without a supercharger are called normally aspirated, or naturally aspirated. They are solely dependent on the ambient pressure of the air, and therefore, aircraft with normally aspirated engines will reduce in power output as their altitude increases and the ambient air pressure reduces. Therefore, they produce maximum power at low altitudes.

Aircraft piston engines are often augmented by turbochargers to increase their power output at higher altitudes, but, unlike car engines, at lower altitudes we do not want the engine to be too powerful as that would put unnecessary stress on the engine and could result in higher wear/greater chance of failure. Therefore, aircraft engines use "altitude boosted" turbochargers, that maintain the same level of power from the ground up until a higher altitude, and after that, when the turbocharger can no longer maintain sea level manifold pressure, the power begins to decrease.

Therefore, the correct answer here is "normally aspirated", as only this type of engine produces its greatest amount of power at low altitude and has a constant decrease with altitude. Both superchargers and turbochargers would be able to maintain the same power output to higher altitudes, and an ailing engine just means that it is damaged or worn and is not working at peak condition.