Note from dshort: I've updated the quiz based on yesterday's Q3 Financial Accounts of the United States (previously referred to as the Flow of Funds Accounts). Hint: The correct answer is the same as it was for the last quiz, just more incredible.

Pop Quiz! Without recourse to your text, your notes or a Google search, what line item is the largest asset on Uncle Sam's balance sheet?

The correct answer, as of the latest quarterly data, is ... Student Loans.

The rapid growth in student debt has been an ongoing topic in the financial press. One stunning chart that continues to haunt me illustrates the rapid growth in federal loans to students since the onset of the great recession. Here is a chart based on data from the Financial Accounts Table L.105, which shows the Federal Government's assets and liabilities.

As I point out on the chart, the two callouts are for Q4 2007, the quarter in which the Great Recession began (December 2007) the most recent quarter on record, Q3 2013. The loan balance has risen and astonishing 517 percent over that timeframe, most of which dates from after the recession.

This chart only includes federal loans to students. Private loans make up an even larger amount. See this Bloomberg article pubished in June that highlights the larger problem:

• $1 Trillion Debt Crushes Business Dreams of U.S. Students

But back to our quiz. Student loans may be a liability on the consumer balance sheet, but they constitute an asset for Uncle Sam. Just how big? It's 44.4 percent of the total federal assets, up from 42.0% last quarter. This is about 6.3 times larger than the 7.1 percent for the Total Mortgages outstanding and 4.4 times the size of Taxes Receivable.

Of course, assets are, sadly, the trivial side of Uncle Sam's Financial Accounts balance sheet -- about 1.61 Trillion. The liability side totaled 15.71 Trillion at the end of Q3.

As I type this, the S&P 500 is at its all-time high. However, the student loan bubble, the biggest slice in Uncle Sam's asset pie, will haunt us for many years to come.

Closing note: For a fascinating slide set on student debt, see this presentation (PDF format) by Donghoon Lee, a Senior Economist at the Federal Reserve Bank of New York.