What role did credit and speculation play in the stock market crash?

For the answer to the question above asking what role did credit and speculation play in the stock market crash? I think you are referring to wall street crash of 1929
Too much credit is not good for the economy. the people keep on borrowing while they have no jobs to pay the interest on the loans and credit.
In return, the company and the bank cannot collect money from them.In Speculation, players buy and sell shares of stock, trying to have the most money at the end of the game which is a high risk way of trading stocks. when the banks collapse the traders are so afraid that the  economy will collapse then they start selling their stocks which resulted to depression.

This answer would be c