Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Let me give you an example: Context: Architecturally, the school has a Catholic character. Atop the Main Building's gold dome is a golden statue of the Virgin Mary. Immediately in front of the Main Building and facing it, is a copper statue of Christ with arms upraised with the legend 'Venite Ad Me Omnes'. Next to the Main Building is the Basilica of the Sacred Heart. Immediately behind the basilica is the Grotto, a Marian place of prayer and reflection. It is a replica of the grotto at Lourdes, France where the Virgin Mary reputedly appeared to Saint Bernadette Soubirous in 1858. At the end of the main drive (and in a direct line that connects through 3 statues and the Gold Dome), is a simple, modern stone statue of Mary.
Question: To whom did the Virgin Mary allegedly appear in 1858 in Lourdes France?
The answer to this example can be: Saint Bernadette Soubirous
Here is why: This is the correct answer. Because the question is asking for the name of the person and following sentence from the passage answers it: It is a replica of the grotto at Lourdes, France where the Virgin Mary reputedly appeared to Saint Bernadette Soubirous in 1858.

OK. solve this:
Context: Warming homes and other buildings is an obvious way that thermal energy can be used. Two common types of home heating systems are hot-water and warm-air heating systems. Both types are described below. You can watch an animation showing how a solar heating system works at this URL: A hot-water heating system uses thermal energy to heat water and then pumps the hot water throughout the building in a system of pipes and radiators. You can see a diagram of this type of heating system in Figure 18.12. Typically, the water is heated in a boiler that burns natural gas or heating oil. There is usually a radiator in each room that gets warm when the hot water flows through it. The radiator transfers thermal energy to the air around it by conduction and radiation. The warm air then circulates throughout the room in convection currents. The hot water cools as it flows through the system and transfers its thermal energy. When it finally returns to the boiler, it is heated again and the cycle repeats. A warm-air heating system uses thermal energy to heat air. It then forces the warm air through a system of ducts. You can see a diagram of this type of heating system in Figure 18.13. Typically, the air is heated in a furnace that burns natural gas or heating oil. When the air is warm, a fan blows it through the ducts and out through vents that are located in each room. Warm air blowing out of a vent moves across the room, pushing cold air out of the way. The cold air enters an intake vent on the opposite side of the room and returns to the furnace with the help of another fan. In the furnace, the cold air is heated, and the cycle repeats. Its easy to see how thermal energy can be used to keep things warm. But did you know that thermal energy can also be used to keep things cool? Cooling systems such as air conditioners and refrigerators transfer thermal energy in order to keep homes and cars cool or to keep food cold. In a refrigerator, for example, thermal energy is transferred from the cool air inside the refrigerator to the warmer air in the kitchen. You read in this chapters "Transfer of Thermal Energy" lesson that thermal energy always moves from a warmer area to a cooler area, so how can it move from the cooler refrigerator to the warmer room? The answer is work. The refrigerator does work to transfer thermal energy in this way. Doing this work takes energy, which is usually provided by electricity. Figure 18.14 explains how a refrigerator does its work. For an animated demonstration of how a refrigerator works, go to this URL: The key to how a refrigerator or other cooling system works is the refrigerant. A refrigerant is a substance, such as FreonTM, that has a low boiling point and changes between liquid and gaseous states as it passes through the cooling system. As a liquid, the refrigerant absorbs thermal energy from the cool air inside the refrigerator and changes to a gas. As a gas, it releases thermal energy to the warm air outside the refrigerator and changes back to a liquid. A combustion engine is a complex machine that burns fuel to produce thermal energy and then uses the energy to do work. Two basic types of combustion engines are external and internal combustion engines. An external combustion engine burns fuel externally, or outside the engine. The burning fuel releases thermal energy that is used to turn water to steam. The pressure of the steam is then used to move a piston back and forth in a cylinder. The kinetic energy of the moving piston can be used to turn a turbine or other device. Figure 18.15 explains in greater detail how this type of engine works. You can see an animated version of an external combustion engine at this URL: [Link] . An internal combustion engine (see Figure 18.16) burns fuel internally, or inside the engine. This type of engine is found in most cars and other motor vehicles. It works in these steps, which keep repeating: 1. A mixture of fuel and air is pulled into a cylinder through a
Question: complex machine that produces thermal energy outside the machine and uses the thermal energy to do
Answer:
external combustion engine