The conclusion that can be drawn from the graph is that in most years, the U.S. federal budget did not show a surplus, and that the trend of government spending and revenue generally followed the same pattern until around 2008, when spending increased and revenue decreased. This suggests that the federal budget was unbalanced for much of the time period shown in the graph.
Therefore, options A, B, and C are not supported by the graph. The graph does not show that federal law requires the budget to be balanced or that politicians did a good job in balancing the budget, nor does it show that there were mostly surpluses in the federal budget.
Option D, which suggests that the graph shows a mostly unbalanced budget, is the most accurate conclusion that can be drawn from the information provided.