The fourth alternative is correct (D).
Monopolization was not a cause of the Great Depression, because monopolies exist in a timely manner. A monopoly exists when only one company offers a good or service.
The causes of the Great Depression of 1930 are overproduction - which has not found enough demand in the world. Another factor was the credit released by the banks in a discretionary manner, which has identified many companies. And finally, the high expenses of government and people, generating uncontrolled expenses. All of this has resulted in the biggest crisis the US has ever experienced.
