What was a leading cause of the Great Depression?

Buy stocks on margin with money people did not have

Stock prices dropped so much that only the poor could buy them, causing a protest among the middle and upper classes

Germany failed to pay back all of the Reparation money owed to the Allies by October, 1929

President Hoover withdrawing his money before the public knew about the expected Crash, leading many into a panic because they thought he was getting "too rich" for the 1920s