A． The exterior surrounding air is heated．
B． The building materials are very expensive．
C． Construction time is increased．
D． Extra air-conditioning equipment is needed．
A． The poor reception of radio and TV signals．
B． The removal of trees and grass from building sites．
C． The harmful effects on the city's plants．
D． The obstruction of air traffic．
A． Electricians
B． Environmentalists
C． City planners
D． Television viewers
A． Skyscrapers provide more usable space than other buildings．
B． The skyscrapers first appeared in the late 1960s．
C． Where there are skyscrapers, television reception is poor．
D． The two World Trade Center towers are skyscrapers．