What caused the U. S. stock market to crash in 1929

The 1920's were known as the roaring 20's. Investors got confident in the market and bought stocks on margin. More and more investors had borrowed money to get into the stock market. When the stock market turned downed, that forced investors to sell rapidly. However, there were no buyers to offset those trades. Therefore, there was a supply and demand in balance, which directly causes the stock market to crash.

A) they couldnt pay back loans