Question

which of these faults, if any, were formed under compression?
a
b
c
a and b

Explanation:

In geology, reverse faults are formed under compressional stress. Compression causes one block of rock to be pushed up over another. By observing the fault - types in the images, we identify the one with characteristics of a reverse fault which is formed under compression.

Answer:

(Without seeing the specific fault - type details in the images, we can't give a definite letter answer. But the general knowledge is that reverse faults are formed under compression. If one of the images shows a reverse fault, that would be the answer.)