The primary reason it rains more heavily on the windward side of mountain ranges is due to the interaction of prevailing winds with the topography of the mountains.
When warm, moist air from the ocean (or nearby bodies of water) is pushed toward the mountains by prevailing winds, it rises as it encounters the elevated terrain. As the air rises, it expands and cools, leading to condensation of moisture and the formation of clouds. This process results in precipitation, which falls predominantly on the windward side of the mountain range.
Thus, the most accurate explanation among the options provided is:
Prevailing winds bring warm, moist air masses from sea level to high altitudes, cooling the air and causing rain.
This statement captures the key aspects of orographic rainfall, where the lifting of air due to the terrain leads to increased precipitation on the windward side.