Which fact is the best piece of supporting evidence that overproduction and falling prices was a cause of the great depression? a) in 1930 over 1,350 banks closed and customers lost all their savings. b) the unemployment rate in 1929 was 3.2% and by 1933 there was a 25% unemployment rate. c) in 1920 a bushel of wheat sold for $2.94, in 1929 it sold for $1.00 and by 1932 a bushel sold for .30 cents. d) the stock market's dow average dropped over 23% over a two day period in october of 1929 and lost 90% of it's value by 1932.