Answer:
b. Regulations were relaxed, leading to nonqualifying mortgages getting approved for loans.
c. Real estate appraisers and rating agencies were lax
d. Credit default swaps claimed to insure CDOs.
Explanation:
Home buyers actually never opted for traditional fixed-rate mortgages, since they chose adjustable rate mortgages and optional ARMs, which allowed them to make low coupon payments for the first two years and reset later. Whereas some borrowers didn't understand the payment structure while some thought that the home prices would go up and they would profit through refinancing or sale.