The problem raised by the author in solid waste treatment and reuse is ______.

A．some people are trying to solve their waste problems
B．the government is not concerned with the problem of wastes
C．recovered materials won't be able to compete with new materials
D．citizens will unwillingly pay the costs of changing the waste system

A．there was a special plant to treat the polluted air
B．the city was away from the mainland
C．people in the city did not burn oil or coal
D．vehicles there were powered by electricity