Why Are Maritime Air Masses from the North Atlantic of Only

Why are maritime air masses from the north Atlantic of only limited concern for weather in the U.S.?

A) Question is incorrect; these air masses are very important.
B) Temperatures are usually mild over this region.
C) They never cause severe storms.
D) Prevailing winds move them away from the U.S.
E) Polar fronts block these air masses from the U.S.