The graph shows monthly temperature data, in degrees Celsius (°C),

Official Explanation

Taken by itself, the graph and its line of best fit support the conclusion that Earth’s mean tropospheric temperature declined over the 8-year period shown. Given that the data are already plotted monthly, adding labels for months to the axis would not change the data plotted in the graph. Since none of the data points stray beyond the currently plotted area on the vertical axis, there is no clear reason to broaden the range of that axis, and, even if it were broadened, the trend shown in the graph would remain the same. Given that mean tropospheric temperature is the only characteristic in question, additional characteristics are not likely to have any effect on the trend shown in the graph. However, if tropospheric temperature readings from other satellites were very similar to those shown in the graph, the conclusion drawn on the basis of the graph would be strengthened, and if those other readings were instead different from those shown in the graph, the conclusion could be weakened.

The correct answer is tropospheric temperature readings from other satellites.

For a revision of data points toward the line of best fit to weaken the conclusion that Earth’s mean tropospheric temperature declined over the 8-year period, it would have to result in some of the lowest temperatures toward the latter part of the 8 years being revised upward or some of the highest temperatures in the earlier years being revised downward. This would lessen the negative slope or result in a positive slope of the line of best fit. Since the low temperatures in 2008 are significantly further from the best-fit line than the highest temperatures in 2001, the greatest increase in slope in the best-fit line would result from revising temperatures in 2008 toward the current best-fit line.

The correct answer is 2008.