Answer:
B. a warm coat, because the winters will be cold
Explanation:
Continental climates are notable for extreme weather conditions. When it is hot, it is extremely hot and when it is cold, it is extremely cold. Tropical climates on the other hand are known to always have hot weather conditions.
Since Harry is already used to the tropical climate which largely features hot temperatures, we assume that he already has suitable clothing for such weather conditions. So, in addition to that, Harry would need warm clothing for the cold winters which he would experience in the continental climate. So, Harry would need a warm coat because the winter will be cold.