The correct answer is answer D ("Relatively brief").
If we look at unemployment statistics in post-great depression-era as a whole, most categories show an improvement in comparisson to the numbers of the Great Depression, including length of unemployment.
However, this particular statistic has seen various peaks throughout modern U.S. economy's history. That's why saying that now is more brief has to be taken as a relative statement. For example, as noted by the Wall Street Journal in July of 2009 "The average length of unemployment is higher than it’s been since government began tracking the data in 1948".
Hope this helps!