15. Read the text and fill in the gaps transforming capitalized words. The London Underground was the (1) world. It is over 140 years old. Its construc- tion (2) in 1860. It opened in 1863 and was only 4 miles long (6.5 kilometres). It was not very deep and steam trains were used. Then (3) tunnels were built and in 1890 the electric railway was opened. (4) called this system the Tube and it is still a very popular name for the London Underground. Some of its deep stations were used for (5) of the (6) during the World War II. A great number of people use the underground system every day because it connects nearly all the parts of this mag- nificent city. It is not only the (7) in the world, but it is one of the most mod- ern systems with its eleven lines which cover London.