3.The indoor air pollution is caused by _______.

A. the limit of the flow of air between inside and outside

B. the building way that the builders want to save energy

C. the building things that are made of man-made materials

D. the man-made building materials and the limit of air-flow

4.The reason why we should use different kinds of plants to clean the air is that _______.

A. plants can let out all kinds of pollutants indoors

B. plants may take in more oxygen which people need

C. plants can absorb some kinds of harmful indoor chemicals

D. plants can make our houses prettier and more healthy

Metro Pocket Guide

Metrorail(地铁)

　Each passenger needs a farecard to enter and go out. Up to two children under five may travel free with a paying customer.

　Farecard machine are in every station, Bring small bills because there are no change machines in the station and farecard machine only provide up to $ 5 in change.

　Get one of unlimited Metrorail rides with a One Day Pass. Buy it from a farecard machine in Metro stations. Use it after 9:30 a.m. until closing on weekdays, and all day on weekends and holidays.

Hours of Service

Open: 5 a.m. Mon-Fri 7a.m. Sat-Sun.

Close midnight Sun-Thur. 3. a.m. Fri- Sat. nights

　Last train times vary. To avoid missing the last train, please check the last train time posted in the station.

Metrobus

　When paying with exact change, the fare is $ 1.35. When paying with a SmartTrip card the fare is $1.25

Fares for the Senior /disabled customers

Senior citizens 65 and older and disabled customers may ride for half the regular fare. On Metrorail and Metrobus, use a senior/disabled farecard or SmartTrip card. For more information about buying