The Reason Why the Deposit Insurance Has Worked Well for So

The reason why the deposit insurance has worked well for so long and its risk-taking incentive problems surfaced only recently is that

A) the banks were not aware of the risk-taking issue and have begun to understand it only recently.
B) the banks were less greedy in the early era of the institutionalization of the deposit insurance.
C) the banks' risk-taking propensity depends on the values of their charter and recent deregulation lowers the values of their charter.
D) the banks' risk-taking propensity increases over time.
E) none of the above