To determine the absolute age of rocks and fossils, geologists use
stratigraphy
the identification of periods of glaciation
the rates of decay of radioactive elements
the order in which rock layers occur

The right answer is C. The rates of decay of radioactive elements.

The dating methods make it possible to locate an object in time, fossil remains, and to estimate a date as accurate as possible. If Carbon 14 is the method that comes to mind instantly, this is just one method among others. Depending on the object to date, the context of its discovery, the material and the quantity that can be taken, several techniques can be deployed.

Each method of dating is generally dedicated to the study of a type of materials, for example, timber for dendrochronology, organic remains (wood, bone) for the C14 method or lava for the Potassium-Argon method. Some methods are too destructive and/or too expensive, so it may sometimes be preferable to date the sediments surrounding an artifact rather than the object itself.

the fossil record provides evidence of a common ancestor to many species.