Выпишите из текста предложения, которые стоят в страдательном залоге (passive voice). from the history of the london underground the underground railways as a kind of city transport appeared in the second half of the 19th century. the first underground system was proposed by charles pearson in 1843. twenty years later the first line of the london underground was opened for traffic. its length was almost four miles. on that first historic day, 30,000 londoners made the first underground railway travel in the world. in the early days, the trains were driven by steam locomotives, which burnt coal, filling the tunnels with smoke. it is said that the train staff and porters asked for a permission to grow beards and moustaches – as an early form of smog mask. the tunnels of the first underground were made as small as possible in order to reduce the construction costs. the coaches themselves were small and narrow. according to pearson’s project, all lines were laid down close to the ground surface. the deep tunneling came later, in 1890. constructing the tunnel through miles of clay, sand and gravel is no easy task, and it was james henry greathead who developed the method, which made the construction of most london tunnels possible. one of the longest continuous tunnels in the world is the 17½-mile tunnel on the northern line. the first escalator was also installed in the london underground in 1911. during the world war ii, the london underground served as a shelter for thousands of londoners. many british museum treasures spent the war in the tunnels of the underground. the railways were prepared for any emergency that might occur. they had duplicate control systems, repair groups, duplicate power supply and so on. to minimize the danger of flooding the underground near the thames, isolating doors were built in the tunnels. all the trains were equipped with special reduced lighting for using on open sections of track. nowadays the london underground is the most popular means of city transport. its length is about 300 km and it has 273 stations
