You may think that an underground town of 3,500 people is something out of a science-fiction film. You may not believe that such a town has shops car parks, hotels, restaurants, cafes and much more. Well, Coober Pedy in Australia is just such a place. Miners and their families choose to live like this, hoping to get rich looking for the precious stones that Australia is famous for --- opals . Living underground is the only way to be away from the sandstorms and the high temperatures above ground. Deep down in the town far below the desert surface, the temperature is between 19degC and 20degC and life is cool. Mary Deane and her husband Jim are among the lucky ones. They live in a home, built with money from the opals Jim has found. "Whenever people hear we live underground, they always imagine a dusty cave," says Mary, "but they are amazed at my clean kitchen, our furniture and electrical appliances in here." However, not everything is perfect in Coober Pedy. Mary has a tiny garden that she is very proud of, but the grass is not real. Plant life is rare. Water is five times more expensive underground than it is overground. Recycling is a way of life, so Jim usually washes his car with bath water and they have a special system to reuse the water from the dishwasher and washing machine. Even so, most families enjoy life in Coober Pedy. The children can make as much noise as they want and there are no complaints from the neighbors because the thick walls stop sounds from traveling. Adults enjoy the peace and quiet away from the world above. People in Coober Pedy live underground  _  .
because of their secret identities because it is warmer underground so that they can save some money due to the terrible natural environment.
Question: You may think that an underground town of 3,500 people is something out of a science-fiction film. You may not believe that such a town has shops car parks, hotels, restaurants, cafes and much more. Well, Coober Pedy in Australia is just such a place. Miners and their families choose to live like this, hoping to get rich looking for the precious stones that Australia is famous for --- opals . Living underground is the only way to be away from the sandstorms and the high temperatures above ground. Deep down in the town far below the desert surface, the temperature is between 19degC and 20degC and life is cool. Mary Deane and her husband Jim are among the lucky ones. They live in a home, built with money from the opals Jim has found. "Whenever people hear we live underground, they always imagine a dusty cave," says Mary, "but they are amazed at my clean kitchen, our furniture and electrical appliances in here." However, not everything is perfect in Coober Pedy. Mary has a tiny garden that she is very proud of, but the grass is not real. Plant life is rare. Water is five times more expensive underground than it is overground. Recycling is a way of life, so Jim usually washes his car with bath water and they have a special system to reuse the water from the dishwasher and washing machine. Even so, most families enjoy life in Coober Pedy. The children can make as much noise as they want and there are no complaints from the neighbors because the thick walls stop sounds from traveling. Adults enjoy the peace and quiet away from the world above. People in Coober Pedy live underground  _  .
A. because of their secret identities
B. because it is warmer underground
C. so that they can save some money
D. due to the terrible natural environment.
Answer: