The correct answer is B. stratigraphy.
Stratigraphy is the study of rock layers (strata) and layering (stratification). It is used to date fossils by examining the sequence of rock layers in which the fossils are found. By understanding the relative ages of the different layers, scientists can determine the chronological order of the fossils contained within them.
Carbon dating (A) and radiometric dating (C) are specific techniques used for dating organic materials or certain types of rocks, but stratigraphy is the broader method that utilizes the layering of rocks to understand the relative ages of fossils.