In this task, you're given an article, a question which often contains a blank and four options (associated with "A", "B", "C", "D"). Your task is to find the correct answer (from the given options) for the question from the given article and return one of the options from "A", "B", "C", and "D". Do not generate anything else apart from one of the following characters: "A", "B", "C", "D". There is only one correct answer for each question.

Article: Ways to Deal with the Problem of Energy There are different ways in which people try to deal with the problem of energy.One way is the greater production of common energy sources,such as coal,oil and gas.The trouble with these sources,however,is that they are not renewable. Another way is energy conservation ,which means using energy more efficiently.In some very cold countries people build special houses to save energy.They place materials between the inside and the outside of the walls of the house to keep the cold out and warmth in.The house is heated by the lights,the body heat of the people and the other equipment in it. Finally,renewable energy sources are used even though they are often expensive to develop.One form of these is geothermal energy.In certain parts of the world the temperature of the earth increases thirty degrees centigrate with each kilometer down.At six kilometers,therefore,it rises to nearly 200degrees.To get the heat,water is pumped down into the rocks and back up to the surface.Heat from the earth is already used in certain countries.
Question: The writer tells about "the special houses"because they _ .
Options: (A) show the excellent skills of the builders (B) serve as an example of the energy conservation (C) are heated by different sources of energy (D) are warmer than other types of energy
B