|During the twentieth century, there were great improvements in engineering technology.
|These new developments allowed the construction of many amazing tunnels, bridges, towers, and office buildings.
|For centuries, people had dreamed about the possibility of connecting the island of Great Britain to the mainland of Europe.
|However, it was only in 1994 that such a link was completed,
|when a tunnel was dug under the English Channel, between England and France.
|The Channel Tunnel, also known as the “Chunnel”,
|actually consists of three separate railway tunnels.
|These tunnels are about 50 kilometers long.
|They are located about 150 meters below the bottom of the sea.
|Obviously, this was an extremely challenging project to undertake.
|As a result of the Chunnel, it is now possible to travel between London and Paris by train.
|And the trip takes only three hours,
|of which only 20 minutes are spent inside the tunnel!
|A suspension bridge is a bridge that is supported by strong wires that hang from tall towers.
|The world’s longest suspension bridge is the Akashi-Kaikyo bridge, near the city of Kobe, Japan.
|This bridge is nearly 4 kilometers long, and the two towers near the middle of the bridge are about two kilometers apart!
|It took almost 20 years to design this bridge, and 10 years to build it.
|This bridge was designed to withstand extremely strong winds,
|because Japan often experiences wind storms called typhoons.
|The bridge was also designed to withstand powerful earthquakes, which sometimes hit Japan.
|At the beginning of the twenty-first century,
|the world’s tallest free-standing tower was the Canadian National Tower, or the CN Tower.
|The CN tower is 553 meters tall.
|It is located in the city of Toronto, within the Canadian province of Ontario.
|This structure was built in 1975 as a television and radio tower.
|Before the CN tower was built, TV and radio reception in the Toronto area was poor.
|This was because the TV and radio signals were blocked by the buildings of downtown Toronto.
|When the CN tower was built, this problem was solved.
|Of course, the CN tower is also a famous tourist attraction.
|People can ride in the very fast elevators that take them to observation areas,
|which are at about 350 and 450 meters above the ground.
|Although the CN Tower is the world’s tallest tower, it is not an office building.
|The tallest buildings in the world are the Petronas Towers, in the city of Kuala Lumpur, Malaysia,
|and the Sears Tower, in the American city of Chicago.
|The Sears Tower, which is 442 meters tall, was completed in 1974.
|It has 110 floors, and its top floor is the highest office floor in the world.
|However, the Petronas Towers reach slightly higher, to a height of 452 meters.
|The Petronas Towers were completed in 1998.
|Obviously, the late twentieth century witnessed some amazing achievements of engineering.
|It will be very interesting to see what new wonders will be constructed in the twenty-first century!