In a big city， its hard to get around. Underground trains can help us. They are a part of city life. Are there underground trains in your city？ Lets find more facts about underground.

There are three main words for underground trains. One is just “underground”， one is “metro” and one is “subway”. Many logos（標志） come from these different names.

This is true in Beijing too. The inside part of the logo is a D. Its from the Chinese word： Di Tie（地鐵）.

The underground started running in 1863. London was the first city to get underground trains. About half of the trains are now above the ground. The fares（票價） are expensive. But children under 11 can travel free with an adult（成年人）.

New York Subways are the worlds largest and busiest subway system（系統(tǒng)）. They run 24 hours a day， and 365 days a year——the only one in the world.

In the subways， you can often enjoy singing， dancing and other performances（表演）.

This metro is in Moscow， Russia（俄羅斯的莫斯科）. There are many artworks（藝術(shù)品） inside. Its a very beautiful “underground palace（宮殿）”.

The metro is very deep（深的） under the ground. The deepest part is 84 meters deep， as high as a 28-storey building. It was a place for people in wartime（戰(zhàn)時） to hide（躲避） from the air attacks（空襲）.