The has rich deposits of loess soils. A.
Gobi Desert
B.
Sahara Desert
C.
Kyzylkum Desert
D.
Karakum Desert

I’m so sorry and I just got cheated on me and b

I think it’s b correct me if I’m wrong

Bcold,less-dense air falls

The highest point of a hill (or mountain) is a single point.
a single point can only be precisely marked with a dot. 
putting on a contour line is impossible  on a single point because the contour line is created after multiple points that have the same hight are marked, and after that, all of those points are connected with a line that creates a closed area. so the highest point, as said above, is a single point, there are no other points with the same height, so the only possible way for it to be marked is with a dot, and there is no possibility for a contour line.