Huangshan has an average of 255.9 foggy days every year. Generally speaking, November to May of the following year is the best time to watch the sea of clouds in Huangshan, especially after rainy and snowy days, and before sunrise and sunset, the sea of clouds must be the most spectacular. So d is wrong.

Huangshan Mountain is mainly composed of Yanshanian granite, with developed vertical joints, strong erosion and cutting, criss-crossing fractures and fissures, and long-term corrosion by water, forming magnificent granite caves and tunnels, which make it a ridge canyon, with 3 ridges, 22 rocks, 7 rocks and 2 passes everywhere. The joints of Qianshan rock mass are sparse, the rocks are spherically weathered, and the mountains are magnificent; The joints of Houshan rock mass are dense, mostly vertically weathered, and the mountain is steep, forming the landform characteristics of "majestic front mountain and beautiful back mountain". So c is right.