Passage Two Questions 29 to 31 are based on the passage you have just heard.

A．There is no greenhouse gas now, since it has been well under control.
B．Now the production of CFCs used in refrigerators is only one third of that in the mid- 1980s.
C．Oxides of sulfur can lead to acid rain and smog.
D．The amount of lead, soot and carbon monoxide that are sent out has been reduced sharply.