Question

when farmers incomes fell due to low prices in the 1920s, they
received credit from banks to repay their loans.
produced more crops to repay their loans.
received credit from the stock market to repay their loans.
were unable repay their loans.

Explanation:

In the 1920s, when farmers' incomes dropped due to low crop prices, their revenue was insufficient to cover loan repayments. Producing more crops would further lower prices (due to surplus), banks wouldn't lend to repay loans (as farmers were less creditworthy), and the stock market isn't a credit source for farmers. So, they couldn't repay loans.

Answer:

were unable repay their loans.