The highest mountain ranges are formed by geological forces that raise the earth' s crust: two continent-bearing tectonic plates of comparable density collide and crumple upward, causing a thickening of the crust. The erosive forces of wind and precipitation inexorably wear these mountains down. Yet the highest mountain ranges tend to be found in places where these erosive forces are most prevalent. Which one of the following, if true, most helps to reconcile the apparent conflict described above? ['Patterns of extreme wind and precipitation often result from the dramatic differences in elevation commonly found in the highest mountain ranges.', 'Some lower mountain ranges are formed by a different collision process, whereby one tectonic plate simply slides beneath another of lesser density.', 'The amount of precipitation that a given region of the earth receives may vary considerably over the lifetime of an average mountain range.', 'The highest mountain ranges have less erosion-reducing vegetation near their peaks than do other mountain ranges.']