The correct answer is D) the frequency and size of fluctuations around the trend have decreased since World War II.
The statement that is true concerning the historical picture of the business activity in the US is that the frequency and size of fluctuations around the trend have decreased since World War II.
The business fluctuations refer to the cycle of ups and downs in business activities in the country. This fluctuation changes the income of people, change the prices, and the employment rate. Sometimes this cycle prokes recession when people's incomes fall and the level of unemployment rises. After WWII these situations have been less in the United States in comparison with other times in history. The most difficult situation of this regard was the one lived during the economic crisis of 2008.