Choose B, Precipitation
1. The figure shows the snow line trend in the upper reaches of the Yangtze River, which includes the western Sichuan Plateau, the Hengduan Mountains, and the eastern part of the Tibetan Plateau.
2. The graph shows that the higher the latitude the higher the snow line, and the smaller the longitude the higher the snow line. The topography of the upper reaches of the Yangtze River is lower in the southeast than in the northwest, and the strength of the influence of the southeast monsoon is also weakened from southeast to northwest, the amount of precipitation in the region is more in the east than in the west, and more in the south than in the north. The snow line is lower in areas with more precipitation than in areas with less precipitation, so the snow line is lower in the southern part of the eastern part of the region of the upper reaches of the Yangtze River than in the northern part of the western part.
The same example is a comparative map of the snow line on the south and north sides of Mount Everest, where the south side is the windward slope of the southwestern monsoon of South Asia, and the north side is the leeward slope, so the snow line elevation on the south side is lower than that on the north side.? (See illustration, original not found, made one myself.)