What practice in large part caused the stock market crash, sparking the great depression of the 1930s?
a.
banks purchasing a combination of stocks, bonds, and land investments with deposits
b.
people overspeculating on stocks, using borrowed money that they couldn't repay
c.
people buying one stock and selling it the same day, called "day trading"
d.
government investing the taxes it collected in the stock market

B.   people overspeculating on stocks, using borrowed money that they couldn't repay

Explanation:

The Great Depression, also known as the Crisis of the 29th, was a global economic crisis that lasted during the 1930s, in the years before the Second World War. The so-called Great Depression originated in the United States, after the stock market crash on Tuesday, October 29, 1929 (known as Crac's 29 or Black Tuesday, although five days earlier, on October 24, the Thursday Black), and quickly spread to almost every country in the world.