| A.Traffic jams and pollution. |
| B.Population and pollution. |
| C.Overcrowding and traffic jams. |
| D.The poverty and subway problems. |
| A.It made the tunnels larger. |
| B.It put fans in the tunnels. |
| C.It cleaned the chemical gases in the tunnels. |
| D.It reduced the number of passengers riding in the train. |
| A.be troublesome | B.become popular and fashionable |
| C.keep up with | D.seize |
| A.To relocate the workers’ homes outside London,the government built the subway. |
| B.There were so many problems and delays that in 18th century the first subway opened. |
| C.The subway greatly eased the pressure of traffic. |
| D.There were not enough seats for the passengers the first day the subway opened. |