The factor that helped the Great Depression spread to Europe was option C: The United States was loaning money to Germany to pay back Britain and France from World War I.
During the 1920s, the United States became a major creditor to European countries. After World War I, Germany was burdened with significant war reparations that it had to pay to Britain and France. To meet these payments, Germany borrowed heavily from the United States.
However, when the Great Depression hit in 1929, the United States economy collapsed, leading to a decrease in American investments abroad and a decline in international trade. As a result, the United States was unable to continue lending money to Germany, which in turn affected the German economy.
The economic crisis in Germany then spread to other European countries as the German economy was interconnected with other European economies through trade and financial relationships. This interconnectedness and the withdrawal of American loans contributed to the spread of the Great Depression to Europe.
It is important to note that while option A (The United States had borrowed money from Britain and was unable to pay it back) could also be a contributing factor, it is not directly related to the spread of the Great Depression to Europe. The main factor was the United States' loans to Germany and the subsequent impact on the German economy and European countries.