Look at the cause-and-effect diagram. It illustrates an important process in early European history. A cause and effect diagram is shown. In the Cause bubble there is a question mark. In the Effects bubble the following are listed: population growth, increase in trade, development of industry, and revival of towns.

Which of the following was one cause of the four effects shown in the diagram?
A.
spread of religion

B.
invasions of Europe

C.
improvements in farming

D.
development of feudalism