Rock columns

This task is about erosion and weathering.

Question 1Change answer

You are travelling through a desert – sand, sand, and more sand. Suddenly there are 2 huge columns of rock ahead. They look like towers with viewing platforms on the top. 
a)  In the desert, what would cause these rocks to weather?
 
b)  Which letter shows the hardest rock in the column?  ABCDEFGHIJ
 
c)  Which letter shows the softest rock in the column?  ABCDEFGHIJ