Deforestation, that would be clearing the land leading to desertification
Originally it was made from cardboard and wood but now its stone and brick
The answer is d that glaciers erode and pluck from the entirety of the valley floor (including both the floor and walls of the valley) and the result is the U-shape of the ensuing valley as opposed to the typical V shape of valleys resulting from large streams or rivers.
If the world temperature rises by two degrees, mountain glaciers and rivers will start to disappear and mountainous regions will see more landslides, as the permafrost that held them together melts away.
For more info: https://www.google.com/amp/s/news.sky.com/story/amp/what-will-happen-as-the-world-gets-warmer-10336299
