The diagram shows the fossils found in different layers of a rock.

A diagram labeled Fossil Layers is shown. The topmost layer is labeled A and shows the skeleton of a fish, the second layer from the top is labeled B and shows a shell, the third layer from the top is labeled C and shows a fern leaf, and the lowermost layer shows an oak leaf

In which layer is the oldest fossil found?

Group of answer choices

Layer A

Layer B

Layer C

Layer D