When Geologists Determine the Relative Ages of Rocks According to the Principles

When geologists determine the relative ages of rocks according to the principles of stratigraphy,a key assumption is that

A) radioactive isotopes decay at a constant rate.
B) the rocks are more than 20 million years old.
C) the rocks are less than 100 million years old.
D) the rocks have been disturbed only infrequently.
E) the rocks have not been disturbed.