Cory is explain the principle of superposition to his friend which of the following is the best explanation Corey could give

A. Layers of rock are usually made of completely different substances

B. In an area of undisturbed rock the oldest layer of rock will be on the bottom

C.The age of rocks can be determined by the ratio of radioactive isotopes
present

D. To estimate the age of rocks I could really use fossils embedded in the rock layers