Rock layers are correlated if they both contain the same
a. elements
c. fossils
b. shapes
d. type of rock

c. fossils

Explanation:

Fossils are the remains of dead and decayed organisms that are preserved in rocks. Fossils can be preserved using their hard parts, or the products of their activities can remain still for several years.

Fossil are used for relative age dating of rocks.  According to the principle of fossil and fauna succession, it is scientifically correct to correlate areas with the same fossil record because fossils succeed on another in a definite order. All rocks that exists in that time period will contain the organisms that lived during that period in time.