Multiple Choice Identify the choice that best completes the statement or answers the question.
1. Which of the following is the best conclusion that can be made from this graph?
390
Atmospheric Carbon Dioxide
Measured at Mauna Loa, Hawaii
380
370
360
350
Annual Cycle
340
330
320
Jan Apr Jul Oct Jan
1310
1990 2000 2010
1970
1980
1960
a. Atmospheric carbon dioxide levels have been decreasing since
1960.
b. Hawaii has a lot of carbon dioxide.
c. Humans have been working hard to decrease carbon dioxide
levels.
d. Atmospheric carbon dioxide levels have increased steadily since
1960s.