Which of the Following Statements About Carbon Dioxide Levels in Earth's

Multiple Choice

Which of the following statements about carbon dioxide levels in Earth's atmosphere is true?

A) They peaked around 1950 and have been slowly decreasing since then.
B) They are high now but are not higher than the highest estimated levels during the last 420,000 years.
C) They are estimated to be higher now than at any time in the past 420,000 years.
D) They began to decrease when the use of CFCs stopped.