The Hudson Bay, unlike the other choices, is not a tropical area. The question asks which is not an area where maritime tropical air masses form that affect North America. While the air masses formed at the Hudson Bay would still affect North America, it is not a tropical mass that is formed. Also the term "maritime" means bordering or near the sea, and only a portion of the Hudson Bays is just that. That is why the correct answer is C. I did the test as well and can confirm that this is correct.
