The correct answer is:
D) As stock prices began to drop, more brokers made "margin calls" which led to more devaluing of stock as panic set in as shares flooded the market.
Before the crash of 1929, almost 40 cents of every dollar loaned in America was applied to buying stocks, usually through margin investing. When the market began to fall, brokers started to execute their margin calls and borrowers were frequently incapable of paying up. In those cases, brokers just sold those stocks, wiping out savings and rising panic.