機器
environmental
air
air conditioning
air pollution
aire
and
auto
beijing
bumper
busy
capital
car
carbon
carrier
community
construct
del
diesel
dioxide
drive
ecology
environment
gas
hazard
jam
lorry
metropolis
metropolitan
nature
outer
part
polluted
pollution
problem
progress
road
schoolboy
semi
smoke
spare
traffic
transport
transportation
vehicle
way
weather