A geologist finds four layers of sedimentary rock. She determines that no geologic events have shifted the layers. She labels the layers A, B, C, and D from the top to the bottom.Which statement about these layers is accurate?

In undisturbed sedimentary rock, the law of superposition says that lower layers are older than the layers above them. From top to bottom, the order is A, B, C, D, so D is oldest and A is youngest. Therefore, B is younger than D; the other statements reverse the age order.

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