In 1901,H.G.Wells,an English writer,wrote a book describing a trip to the moon.When the explorers landed on the moon,they discovered that the moon was full of underground cities.They expressed their surprise to the “moon people” they met.In turn,the “moon people” expressed their surprise.“Why,” they asked,“are you traveling to outer space when you even don’t use your own space?”
H.G.Wells could only imagine travel to the moon.In 1969,human beings really did land on the moon.People today know that there are no underground cities on the moon.However,the question that the “moon people” asked is still an interesting one.A growing number of scientists are seriously thinking about it.
Underground systems are already in place.Many cities have underground car parks.In some cities,such as Tokyo,Seoul and Montreal,there are large underground shopping areas.The “Chunnel”,a tunnel connecting England and France,is another representative project of underground systems.