Why is the amount of water that goes over Niagara Falls today only about half as much as went over the falls a century ago?

even though you have attached neither the chart nor the generalizations, i have located them online. the right answer is d, since they are asking you about a generalization. you can only infer from the chart that between 2008 and 2009 the number of employed workers decreased significantly (from over 115 millions to 107 millions approximately), which signals some type of economic crisis.  

answer; the president uses mass media to gain support for policies;