In 1863 the first underground passenger railway in the world opened in London. It ran for just under seven kilometers and allowed people to avoid terrible __41__(crowd) on the roads above as they travelled to and ___42__ word. It took three years to complete and was built using an interesting method. This included digging up the road, ____43___(lay) the track and then building a strong roof over___44___ top. When all those had been done, the road surface was replaced.
    Steam engines ___45__(use) to pull the carriages and it must have been___46__(fair)unpleasant for the passsengers, with all the smoke and noise. However, the railway quickly proved to be a great success and within six months, more than 25,000 people were using___47__ every day.
    Later, engineers ____48___(manage) to construct railways in a system of deep tunnels (隧道）, which became known to the tube. This development was only possible with the ___49___ (introduce) of electric-powered engines and lifts. The central London Railway was one of the most ___50___(success) of these new lines, and was opened in 1900. It had white-painted tunnels and bright red carriages, and proved extremely popular with the public.