I'm pretty sure it's C, it makes the most sense.
The variety of climatic zones on a mountain are due primarily to differences in rainfall created by the rainshadow effect and relief rainfall. The mountain acts as a barrier to moving air causing it to rise. As the air rises it cools and condenses to form clouds and rainfall on one side of the mountain. As the air rises and starts to descend down the other side of the mountain, it is drier, producing less rainfall on this side. The side receiving rainfall is called the windward side and the side getting little rain is the leeward side.
