Which of the Following Is a Macroeconomic Topic

Which of the following is a macroeconomic topic?

A) The gasoline tax in Oregon is one of the highest in the United States.
B) Real gross domestic product in the United States decreased by about 1.5 percent between 2009 and 2010.
C) The cost of medical care in the United States is much higher than identical care in Canada.
D) If the government subsidizes vaccinations, fewer children will contract smallpox.