Your answer is C..
if this answer is incorrect, then i am sorry..
Answer: The mild conditions this winter are driven by a "positive phase" of the Arctic Oscillation, which strengthens the jet stream, a ribbon of fast-moving air that flows west to east over the Northern Hemisphere. Changes in the jet stream's behavior can have a profound impact on weather systems around the world.
Explanation:
It would be the conclusion.
Asked? Or challenged I would say