The correct answer is C. risky banking practices.
Although all of the options listed may have contributed to economic difficulties during the Great Depression, risky banking practices were a major cause of the financial collapse. During the 1920s, many banks made risky investments and loans, which created a bubble in the stock market and an overall economic boom. However, when the stock market crashed in 1929, many banks lost money and were unable to repay their depositors, causing a wave of bank failures and a widespread loss of confidence in the financial system. This led to a decrease in consumer spending and investment, which ultimately worsened the economic downturn and created the Great Depression.