How did the stock market crash of 1929 start

The stock market crash of 1929 was the result of heavy borrowing by consumer investors. The roaring 20's defined a period of time in which the market and the economy grew at a rapid rate. When the stock market corrected down, most of the investors who had margin loans were caught by surprise. This "margin squeeze" became the beginning of the end.

d is the answer. leo should include the source.