What is the difference between expressed and implied powers?

What would lead a historian to consider two events to have a relationship of correlation rather than causation

Which factor has played the most important role in changing the way history is studied over time?

How did the russian revolution impact world war i? a) the russians required the allied powers to come to their aid and defeat the radical groups. b) the russians pulled out from the war, enabling the germans to focus on the western front. c) the russians created new technological advancements that were used by the allied powers to win. d) the russians created a new communist government that aligned with the central powers instead.