I believe the correct answer would be B. nations were competing to build strong economies and large Empires.
I came to this conclusion through process of elimination. It would be impossible for the answer to be A because your question refers to how tensions rose before World War I, but the Bolsheviks in Russia did not take power until World War I was nearly over.
I do not believe the answer would be C. because the United States was hardly involved in the European conflicts until years later.
I don't think the answer is D. either because Christianity was clearly the dominant religion at the time. There was no arguing that.