Read the excerpt from "Climate Change: An Overview.”By the early twentieth century, carbon emissions from fossil-fuel burning reached 1 billion tons a year. Automobiles, airplanes, and domestic and agricultural energy demands all contributed to the rising trend. In the 1950s, scientists used a new generation of equipment to confirm that carbon-dioxide concentrations were doubling and that this would have the effect of increased temperatures.
Answer
A
the increase in automobile usage from the early twentieth century through the 1950s
B
the changes in carbon dioxide emissions from the early twentieth century through the 1950s
C
the development of new technologies from the early twentieth century through the 1950s
D
the changes in popular modes of transportation from the early twentieth century through the 1950s
Explanation
The excerpt traces rising carbon emissions from fossil-fuel use, reaching 1 billion tons a year by the early twentieth century, and then describes scientists confirming that carbon-dioxide concentrations were doubling in the 1950s. Automobiles and other energy uses are mentioned as contributors, while new equipment is mentioned as a way to measure the change. So the main focus is changes in carbon dioxide emissions and concentrations, not transportation or technology alone.
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