The correct answer is - C. the windward side.
The windward side of the mountain is the side that faces the ocean. This side is the side of the mountain that gets the moisture-rich air from the ocean, which is also very often warm as well.
This results in the windward side of the mountain being a rainy and moist area. The other side of the mountain though, the leeward side, will be getting very little rain and moisture because the windward side is blocking it, so it will mostly get dry air masses.