The London underground system has the (1)            of being the oldest and most complex underground system in the world. Before 1850, train services to London had already been (2)          ,but people couldn' t build railways into the city because doing that would cause great (3)           to many historic buildings.

So many buses were needed to (4)            people to the city centre, which, however, often (5)              traffic. This problem led to the development of the underground system.

In 1854, Metropolitan Railway Company was allowed to build an underground railway and the first, tunnels were opened in 1863. In 1868, the next (6)           of the underground system was opened by another company called the Metropolitan District Railway