Why did housing prices rise rapidly during 2002 - 2005?

Why did the mortgage default rate increase so sharply during 2006 and 2007 even before the 2008 - 2009 recession began?

Explain how a bonds interest rate can change over time even if interest rates in the economy do not change.

What is the primary risk of trading in the fed funds markets? How did this risk come into play during the financial crisis of 2008-2009?