Which of the following contributed to the nation's economic crisis that began in 2007?

Which of the following contributed to the nation's economic crisis that began in 2007?
 
  a. The influence peddling scheme of the Keating five which led to a housing bubble.
  b. Deregulation of financial institutions, which allowed them to engage in risky practices such as subprimemortgages.
 c. The collapse of hundreds of savings and loan institutions, which had a ripple effect throughout the Americaneconomic system.
 d. Overregulation of Wall Street, which began in the Clinton administration, eventually paralyzed credit markets.