2008-09 great recession questions

1. what was the final "domino" effect to the eventual crash and start of the recession in 2008 ? why would this failure within the economy cause so many problems ?

2. what other 2 major factors contributed to the recession ?

3. explain how policy makers of 2008 learned from the great depression. give at least 2 specific examples.

4. explain how the US responded to the great recession of 08-09 by providing at least 3 descriptive examples (policy decisions).

(also technically this isnt business stuff its economics but there is no option for that so i apologise)