Some Challenges in the tropical rainforest is that Deforestation is common and its really bad because they're limiting the rainforest size just to build homes and towns. Basically, Just forgetting about the habitats and the animals and the other tribes.
C. Gobi desert
Is located in east Asia
Hills are easier to climb than mountains. They are less steep and not as high. But, like a mountain, a hill will usually have an obvious summit, which is its highest point. According to the U.S. Geological Survey, there is no official difference between hills and mountains.
Some of them is the indus river and nile river and the Ohio river hope this helped and please gives points