Which of the Following Statements Is True

Which of the following statements is true?

A) Most carbon monoxide produced in the United States comes from internal combustion engines (cars) .
B) Nearly all emissions of sulfur compounds are anthropogenic.
C) Overall, in the past twenty years, air pollution conditions have steadily decreased in most North American and Western European cities.
D) Volatile organic compounds are produced exclusively by human activity.
E) None of these is correct.