What triggered the financial crisis of 2008 in the united states?

a.)global stock markets collapsed.
b.)global industrial production slowed.
c.)american banks stopped making loans.
d.)american housing prices dropped.

I'm very confident on C. The financial crisis of 2008 was one of the worst since The Great Depression. American banks could not make loans because other banks lend when they’re confident that they will be repaid. And in D., housing prices went up.
(Around 31% went to residential property, which pushed up house prices faster than wages.
A further 20% went into commercial real estate (office buildings and other business property)
Around 32% went to the financial sector, and the same financial markets that eventually imploded during the financial crisis.
But just 8% of all the money that banks created in this time went to businesses outside the financial sector.
A further 8% went into credit cards and personal loans.)

Source: positivemoney.org