The correct answer is A) they would own more than they could repay.
A problem for people who bought stock on credit during the 1920s was that if the stock market collapsed, they would own more than they could repay.
And then, it happened. On October 24, 1929, the stock market crashed originating one of the most economically devastating events in the economy of the United States, called the Great Depression. Stocks were overpriced and the crash was imminent. And it did happen. Many people lost their jobs, many fabrics and business closed and most of the Banks declared bankruptcy. What was also disastrous was that many people had bought stock on credit. So the problem for them was that they owned more than they could repay.